Terrorism and the Law

UK Counter-Terrorism Powers: Arrest, Detention, Surveillance and Prevention

The United Kingdom has extensive laws allowing the police, security services and courts to investigate terrorism, disrupt suspected activity and manage people considered to present a continuing risk.

These powers have developed through legislation including the Terrorism Act 2000, Terrorism Prevention and Investigation Measures Act 2011, Counter-Terrorism and Security Act 2015, Investigatory Powers Act 2016, Counter-Terrorism and Border Security Act 2019 and Counter-Terrorism and Sentencing Act 2021.

The Crime and Policing Act 2026 has introduced further changes intended to deal with online activity, young people involved in terrorism investigations, prison conduct and the management of terrorist offenders.

Counter-terrorism powers are deliberately broad, but their use must remain lawful, necessary and proportionate. Courts, Parliament and the Independent Reviewer of Terrorism Legislation provide important scrutiny.

What Is Terrorism?

The Terrorism Act 2000 contains a broad statutory definition of terrorism.

It can include the use or threat of serious action designed to influence a government or international governmental organisation, or to intimidate the public or a section of the public, where the purpose is to advance a political, religious, racial or ideological cause.

The relevant action may involve:

• serious violence against a person;


• serious damage to property;


• endangering another person’s life;


• creating a serious risk to public health or safety; or


• seriously interfering with or disrupting an electronic system.

Different rules can apply where firearms or explosives are used.

Arrest Under the Terrorism Act

Under section 41 of the Terrorism Act 2000, a police officer may arrest without a warrant a person they reasonably suspect to be a terrorist.

A person may also be arrested using ordinary criminal powers where the suspected conduct amounts to another offence.

An arrest does not mean that the person will be charged or convicted. Police must continue investigating and must release the suspect unless there are lawful grounds for continued detention.

Detention Without Charge

A person arrested under section 41 may be detained without charge for longer than someone arrested under ordinary police powers.

The current maximum period is 14 days from the time of arrest.

Continued detention is subject to review and court supervision. The police cannot simply authorise the entire 14-day period at the outset.

Judicial extensions may be sought where further detention is necessary for purposes including:

• obtaining or preserving relevant evidence;


• questioning the suspect;


• examining electronic devices;


• investigating overseas connections;


• analysing financial information;


• identifying other suspects; and


• protecting the public while urgent enquiries continue.

The previous maximum of 28 days ceased to apply in 2011.

Rights During Terrorism Detention

A detained person has important legal rights, including the right to:

• be informed of the reason for the arrest;


• consult a solicitor;


• have someone informed of the detention, subject to lawful delay in limited circumstances;


• receive medical assistance;


• receive interpretation where required;


• be treated in accordance with the applicable custody code; and


• challenge continued detention through the court process.

Special rules may permit access to a solicitor or notification of another person to be delayed in exceptional circumstances. Any restriction must have a lawful basis and cannot be imposed merely for convenience.

Stop and Search Based on Suspicion

Section 43 of the Terrorism Act allows a police officer to stop and search a person whom the officer reasonably suspects to be a terrorist.

The search may be conducted to discover evidence showing that the person is involved in the commission, preparation or instigation of terrorism.

Reasonable suspicion must be based on objective grounds. It cannot lawfully be based solely on a person's:

• race;


• religion;


• nationality;


• clothing;


• political views; or


• presence in a particular community.

Stop and Search Without Individual Suspicion

Section 47A permits stop and search without reasonable suspicion of the individual, but only within an authorised area and for a limited period.

A senior officer must reasonably suspect that an act of terrorism will take place and consider the authorisation necessary to prevent it.

Within the authorised area, a uniformed officer may search people or vehicles for evidence connected with terrorism without first establishing suspicion against each individual.

This is intended as an exceptional power rather than an ordinary method of policing.

Preparation of Terrorist Acts

Preparing to commit or assist an act of terrorism is a serious criminal offence.

Conduct may include:

• obtaining weapons or explosives;


• researching possible targets;


• conducting hostile reconnaissance;


• constructing a device;


• arranging terrorist training;


• providing logistical assistance;


• preparing travel for terrorist purposes;


• raising or transferring funds; or


• communicating operational instructions.

The maximum sentence for preparation of terrorist acts is life imprisonment.

Failure to Disclose Information

A person may commit an offence if they possess information that they know or believe might be of material assistance in preventing an act of terrorism or securing the apprehension, prosecution or conviction of another person, but fail to disclose it to the police as soon as reasonably practicable.

A reasonable excuse may provide a defence.

The maximum sentence for failure to disclose information about acts of terrorism is now ten years' imprisonment.

This offence does not mean that every rumour, political opinion or vague concern must be reported. The legal test depends on the nature of the information and the person's knowledge or belief.

Proscribed Terrorist Organisations

The Home Secretary may proscribe an organisation believed to be concerned in terrorism where proscription is considered proportionate.

Once an organisation is proscribed, offences can include:

• belonging to the organisation;


• inviting support for it;


• arranging or addressing certain meetings supporting it;


• wearing clothing or displaying an article in circumstances creating reasonable suspicion of membership or support;


• raising or providing funds; and


• making resources available for terrorist purposes.

Membership and inviting support for a proscribed organisation can carry a maximum sentence of 14 years' imprisonment, an unlimited fine or both.

Discussion of an organisation for journalistic, academic, historical or political purposes is not automatically an offence. The precise words, conduct, intention and context matter.

Terrorism Prevention and Investigation Measures

Terrorism Prevention and Investigation Measures, known as TPIMs, replaced control orders in 2011.

A TPIM may be imposed where the Home Secretary is satisfied on the balance of probabilities that an individual is or has been involved in terrorism-related activity and considers the measures necessary for protecting the public.

A TPIM is a civil preventive measure rather than a criminal conviction.

Possible TPIM Restrictions

A TPIM notice may impose restrictions or requirements concerning:

• where the person must live;


• relocation to another area;


• overnight residence;


• electronic monitoring;


• travel outside a specified area;


• possession of travel documents;


• use of telephones, computers and the internet;


• financial services;


• employment or study;


• meetings and communications with specified people;


• reporting to the police;


• attendance at appointments; and


• participation in rehabilitation or disengagement programmes.

The precise measures must be tailored to the risk attributed to the individual.

How Long Can a TPIM Last?

A TPIM notice is generally imposed for one year at a time.

The original legislation normally limited TPIM measures to two years unless there was new terrorism-related activity.

The Counter-Terrorism and Sentencing Act 2021 removed that overall two-year limit. A notice may now be extended in further one-year periods where the statutory tests continue to be met.

This means a TPIM can potentially continue for more than two years, but each extension must be justified and remain subject to court oversight.

Breaching a TPIM

Breaching a TPIM requirement without reasonable excuse is a criminal offence.

A breach involving travel outside the UK can attract particularly serious punishment.

Temporary Exclusion Orders

A Temporary Exclusion Order can be imposed on a British citizen suspected of involvement in terrorism-related activity outside the UK.

Despite its name, the order does not permanently remove the citizen's right to return.

It temporarily requires the person to return only:

• with a permit issued by the authorities;


• under agreed arrangements; or


• following deportation to the UK.

The purpose is to allow a managed return so that the authorities know when and how the person is coming back.

After return, the person may be required to:

• report to a police station;


• notify the authorities of their address;


• attend appointments;


• surrender travel documents; or


• participate in a disengagement programme.

Passport and Travel Restrictions

The authorities may use several powers to prevent or control travel connected with terrorism.

These can include:

• seizing travel documents temporarily at a port;


• refusing or withdrawing a British passport under the royal prerogative;


• imposing travel restrictions through a TPIM;


• using a Temporary Exclusion Order;


• applying for a foreign travel restriction order; and


• using bail or licence conditions following criminal proceedings.

Restrictions must be supported by the relevant legal test and may be open to challenge.

Schedule 7 Border Examinations

Schedule 7 to the Terrorism Act allows specially authorised officers to stop, question, search and, where necessary, detain a person at a port, airport or international rail terminal.

The purpose is to determine whether the person appears to be involved in the commission, preparation or instigation of terrorism.

The officer does not need reasonable suspicion before beginning the examination.

A person can be questioned about matters including:

• their identity;


• travel arrangements;


• where they have been;


• who they have met;


• the purpose of their journey;


• documents and belongings; and


• electronic devices.

How Long Can a Schedule 7 Examination Last?

A person may be examined for up to six hours.

Once the examination reaches the statutory point at which the person is formally detained, additional rights and safeguards apply, including access to legal advice.

Failure to comply with lawful requirements during a Schedule 7 examination can be a criminal offence.

Searches of Electronic Devices

Border officers may examine and, in appropriate circumstances, copy information held on telephones, laptops and other devices.

These powers are controversial because devices can contain substantial amounts of personal, professional and legally sensitive information.

Special considerations may apply to:

• legally privileged communications;


• journalistic material;


• confidential medical information;


• religious material;


• commercially sensitive information; and


• information relating to third parties.

The use of the powers must comply with the statutory code, human rights requirements and applicable safeguards.

Surveillance and Interception

The police and intelligence agencies have extensive investigatory powers, but they cannot lawfully use every form of surveillance without authorisation.

Depending on the activity, powers may include:

• interception of communications;


• acquisition of communications data;


• equipment interference or device hacking;


• covert surveillance;


• use of covert human intelligence sources;


• retention and examination of bulk data;


• access to internet connection records; and


• property interference.

The required authority depends on the intrusiveness of the measure and the agency involved.

The Investigatory Powers Act

The Investigatory Powers Act 2016 provides the principal framework for interception, communications data and equipment interference.

It does not require every internet company automatically to retain the complete content of every person's internet and messaging activity for one year.

Instead, the Secretary of State may issue a retention notice requiring a telecommunications operator to retain specified communications data for a maximum period of 12 months.

Communications data can include information such as:

• who communicated with whom;


• when and for how long communication occurred;


• the service or device used;


• location information; and


• the internet service to which a device is connected.

It does not ordinarily include the content of the message or conversation.

Internet Connection Records

An internet connection record can identify the online service or website domain to which a device connected and when the connection occurred.

It is not intended to provide a complete record of every individual page viewed or the full content entered by the user.

Access to retained data requires lawful authorisation and must be necessary and proportionate for a permitted purpose.

Interception Warrants

Intercepting the content of communications generally requires a warrant.

Many of the most intrusive warrants operate through a "double-lock" system involving:

• authorisation by the Secretary of State or another designated authority; and


• approval by a Judicial Commissioner.

Urgent procedures are available in limited circumstances, but subsequent judicial consideration is required.

End-to-End Encryption

End-to-end encryption means that the content of a message is designed to be readable only on the devices of the sender and intended recipient.

The service provider may be unable to read the message content in an intelligible form.

This presents difficulties for law enforcement, but encryption also protects:

• banking;


• business communications;


• medical information;


• journalists and sources;


• victims of abuse;


• legal communications; and


• ordinary personal privacy.

The legal and technical debate concerns whether providers can assist investigations without creating security weaknesses that expose all users to criminals or hostile states.

Online Terrorist Content

The Online Safety Act 2023 places duties on regulated online services to assess and reduce the risk of illegal terrorist content appearing and spreading through their platforms.

Providers may be required to:

• conduct illegal-content risk assessments;


• introduce proportionate safety systems;


• remove illegal terrorist material swiftly;


• provide reporting and complaints procedures;


• reduce algorithmic promotion of illegal content; and


• cooperate with Ofcom's regulatory requirements.

Ofcom can impose substantial financial penalties where a regulated provider fails to meet its duties.

Platform regulation is separate from the possible criminal liability of the person who creates, possesses or distributes terrorist material.

Viewing and Possessing Terrorist Material

A person may commit an offence by collecting, possessing, viewing or accessing information likely to be useful to someone committing or preparing an act of terrorism.

Defences may apply where the conduct was for purposes including:

• journalism;


• academic research;


• legal work;


• historical study;


• official duties; or


• another reasonable purpose.

The context, frequency of access, nature of the material and the person's explanation will be important.

Sentencing Terrorist Offenders

Serious terrorism offences can result in lengthy determinate sentences, extended sentences or life imprisonment.

Recent legislation has:

• increased maximum sentences for several offences;


• created minimum terms for certain serious terrorist offenders;


• restricted automatic early release;


• extended licence and monitoring arrangements;


• introduced polygraph testing for some offenders; and


• strengthened powers to arrest a terrorist offender suspected of breaching licence conditions.

The precise sentence depends on the offence, the risk posed, the offender's role, their intention and the harm caused or intended.

The Crime and Policing Act 2026

The Crime and Policing Act 2026 includes further counter-terrorism and national security measures.

These include provisions intended to:

• create a youth diversion order for certain young people involved in terrorism-related activity;


• support risk management of young people without relying solely on prosecution;


• strengthen access to online account information for monitoring compliance with national security orders;


• extend certain offences concerning support for proscribed organisations to conduct in prisons and prescribed institutions;


• bring breach of a foreign travel restriction order within the terrorism sentencing and offender-management regime; and


• update powers relating to terrorist offenders in custody or on licence.

Individual provisions may require commencement regulations or supporting guidance before they are fully operational.

Martyn’s Law

The Terrorism (Protection of Premises) Act 2025, commonly known as Martyn's Law, creates duties for certain publicly accessible premises and events to prepare for terrorist attacks.

Depending on capacity and circumstances, duties may include:

• considering evacuation, invacuation and lockdown procedures;


• providing staff information or training;


• appointing responsible persons;


• documenting public protection procedures; and


• taking proportionate measures to reduce vulnerability.

The legislation is directed at preparedness and public safety rather than at creating additional arrest powers against individual suspects.

Organisations should check commencement dates and official guidance before assuming that a particular duty is already enforceable.

Human Rights and Counter-Terrorism

Counter-terrorism measures may interfere with rights concerning:

• liberty;


• privacy;


• family life;


• freedom of expression;


• freedom of association;


• property;


• movement; and


• a fair hearing.

The state may lawfully interfere with some rights to protect national security and public safety, but restrictions must have a legal basis and be necessary and proportionate.

Courts have repeatedly examined counter-terrorism laws to determine whether sufficient safeguards exist.

Independent Review and Oversight

The Independent Reviewer of Terrorism Legislation examines the operation of the principal terrorism laws and reports to the Government and Parliament.

Other oversight is provided by bodies including:

• the courts;


• Parliament;


• the Investigatory Powers Commissioner;


• the Intelligence and Security Committee;


• Ofcom for online-safety duties; and


• the Independent Office for Police Conduct, where relevant.

Oversight does not remove the need for strong powers, but it helps ensure that exceptional powers do not become routine or operate without accountability.

What Should Someone Do if Arrested?

A person arrested or interviewed in connection with terrorism should obtain specialist legal advice immediately.

They should not:

• assume that explaining matters informally is safer than receiving advice;


• delete messages or files;


• contact other suspects;


• breach bail, licence or TPIM requirements;


• give false information; or


• sign a statement they do not understand.

Legal advice at a police station is normally available without charge.

How a Solicitor Can Help

A solicitor experienced in terrorism and national security law may advise on:

• arrest and detention;


• police interviews;


• Schedule 7 examinations;


• searches and seizure of devices;


• TPIM notices;


• Temporary Exclusion Orders;


• proscription offences;


• online terrorist material;


• surveillance and investigatory powers;


• licence conditions;


• terrorism prosecutions;


• human rights challenges; and


• judicial review.

A Balance Between Security and Liberty

The UK already possesses some of the most extensive counter-terrorism powers available in a democratic state.

The central question is therefore not simply whether more powers should be created, but whether existing powers are used effectively, proportionately and with appropriate oversight.

Technology, encrypted communications and online radicalisation continue to create difficult challenges. However, weakening privacy and security for every user may produce risks of its own.

Effective counter-terrorism law must protect the public while preserving the legal safeguards that distinguish lawful investigation from arbitrary state power.

Finding a Terrorism Law Solicitor

Use the search facility at the top of this page to find a criminal defence, terrorism or human rights solicitor who can advise on arrest, detention, border examinations, preventive orders or terrorism charges.

Disclaimer

Solicitors.com is not a firm of solicitors. This article provides general information about counter-terrorism law in the United Kingdom and does not constitute legal advice. The applicable powers, offences and safeguards will depend on the circumstances and the part of the UK involved.

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