The United Kingdom Terror Threat Levels, often referred to as UK Threat Levels, are the alert states that have been in use since 1 August 2006 by the British government to warn of forms of terrorist activity. In September 2010 the threat levels for Northern Ireland-related terrorism were also made available. In July 2019 changes were made to the terrorism threat level system, to reflect the threat posed by all forms of terrorism, irrespective of ideology. There is now a single national threat level describing the threat to the UK, which includes Islamist, Northern Ireland, left-wing and right-wing terrorism. Before 2006, a colour-based alert scheme known as BIKINI state was used. The response indicates how government departments and agencies and their staffs should react to each threat level.

Categories of threat

Since 23 July 2019, the Home Office has reported two different categories of terrorist threat: Previously, since 24 September 2010, the Home Office has reported three different categories of terrorist threat: A fourth category of terrorist threat is also assessed but is not disclosed, relating to threats to sectors of the UK's critical national infrastructure such as the London Underground, National Rail network and power stations. The Joint Terrorism Analysis Centre (JTAC) is responsible for setting the threat level from international terrorism and the Security Service (MI5) is responsible for setting both threat levels related to Northern Ireland. The threat level informs decisions on protective security measures taken by public bodies, the police and the transport sector.

Threat levels

Threat Levels are decided using the following information:

History

Threat levels were originally produced by MI5's Counter-Terrorism Analysis Centre for internal use within the British government. Assessments known as Security Service Threat Reports or Security Service Reports were issued to assess the level of threat to British interests in a given country or region. They had six levels: Imminent, High, Significant, Moderate, Low and Negligible. Following terrorist attacks in Indonesia in 2002, the system was criticised by the Intelligence and Security Committee of Parliament (ISC) as insufficiently clear and needing to be of greater use to "customer departments". The 7 July 2005 London bombings prompted the government to update the threat level system following a recommendation from the ISC that it should deliver "a greater transparency of the threat level and alert systems as a whole, and in particular [it is recommended] that more thought is given to what is put in the public domain about the level of threat and required level of alert." The system was accordingly simplified and made easier to understand. Since 2006, MI5 and the Home Office have published international terrorism threat levels for the entire UK on their websites, and since 2010 they have also published threat levels for Northern Ireland, with separate threat levels for Northern Ireland and the rest of the UK.

2019 'New Reporting Format'

In July 2019 changes were made to the terrorism threat level system creating a 'New Format' of threat levels, to reflect the threat posed by all forms of terrorism, irrespective of ideology. There is now a single national threat level describing the threat to the UK, which includes Islamist, Northern Ireland, left-wing and right-wing terrorism.

Changes to threat levels

The following table records changes to the threat levels from July 2019 – Present:

Old-format historical threat levels

Since 2006, information about the national threat level has been available on the MI5 and Home Office websites. In September 2010 the threat levels for Northern Ireland-related terrorism were also made available. The following table records changes to the threat levels from August 2006 – July 2019 before the 'New Format' was put into place: