UK Threat Levels

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British military personnel guarding Downing Street as part of Operation Temperer following the Manchester Arena bombing.

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. Before then a colour-based alert scheme known as BIKINI state was used.[1] The response indicates how government departments and agencies and their staffs should react to each threat level.

Current threat level[edit]

The current level is "substantial", which was set on 4 November 2019.[2] It was previously reduced to "severe" on 17 September 2017.[3] It had been raised to "critical" following the Parsons Green bombing on 15 September.[4] The previous threat level to that was "severe" having been reduced to that level[5] following an increase to "critical" after the Manchester Arena bombing of 22 May 2017.[6]

The current level of Northern Ireland-related terrorism in Great Britain is "moderate" as of 1 March 2018, having been "substantial" from 11 May 2016.[7] The level was previously raised to Substantial on 25 September 2010 until downgraded on 24 October 2012.[8] The threat in Northern Ireland has been "severe" since 4 March 2009.[9]

On 29 November 2019, due to a terror attack that took place on London Bridge the UK's Government is reviewing the threat level.

Categories of threat[edit]

Since 24 September 2010, the Home Office has reported three different categories of terrorist threat:[10][11]

  • Threat from international terrorism.
  • Terrorism threat related to Northern Ireland in Northern Ireland itself.
  • Terrorism threat related to Northern Ireland in Great Britain (i.e. excluding Northern Ireland).

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.[12]

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.[13] The threat level informs decisions on protective security measures taken by public bodies, the police and the transport sector.[14]

Threat levels[edit]

Threat level Response
Critical An attack is expected imminently.
Maximum protective security measures to meet specific threats and to minimise vulnerability and risk. Critical may also be used if a nuclear attack is expected.
Severe An attack is highly likely.
Additional and sustainable protective security measures reflecting the broad nature of the threat combined with specific business and geographical vulnerabilities and judgements on acceptable risk.
Substantial An attack is a strong possibility.
Moderate An attack is possible, but not likely.
Routine protective security measures appropriate to the business concerned.
Low An attack is unlikely.


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".[15]

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.[16] 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.[13]

Changes to threat levels[edit]

Graph showing the changes in threat levels between 2006 and 2017

The following table records changes to the threat levels since August 2006:[13]

Date National Threat Level Dates International terrorism Northern Ireland related terrorism
1 August 2006 Severe 24 September 2010 – 11 July 2011 Severe GB: substantial NI: severe
10 August 2006 Critical[a] 11 July 2011 – 23 October 2012 Substantial GB: substantial NI: severe
14 August 2006 Severe 24 October 2012 – 29 August 2014 Substantial GB: moderate NI: severe
30 June 2007 Critical[b] 29 August 2014 – 10 May 2016 Severe GB: moderate NI: severe
4 July 2007 Severe 11 May 2016 – 22 May 2017 Severe GB: substantial NI: severe
20 July 2009 Substantial 23 May 2017 – 26 May 2017 Critical GB: substantial NI: severe
22 January 2010 Severe 27 May 2017 – 15 September 2017 Severe GB: substantial NI: severe
11 July 2011 Substantial 15 September 2017 – 17 September 2017 Critical GB: substantial NI: severe
29 August 2014 Severe 17 September 2017 – 1 March 2018 Severe GB: substantial NI: severe
23 May 2017 Critical[c] 1 March 2018 – 23 July 2019 Severe GB: moderate NI: severe
27 May 2017 Severe 23 July 2019 – 4 November 2019 Severe Severe
15 September 2017 Critical[d] 4 November 2019 – Present Substantial Severe
17 September 2017 Severe
4 November 2019 Substantial 29 November 2019 Under review by Government

  1. ^ Threat level increased following the 2006 transatlantic aircraft plot.
  2. ^ Threat level increased following the 2007 Glasgow Airport attack.
  3. ^ Threat level increased following the Manchester Arena bombing.
  4. ^ Threat level increased following the Parsons Green bombing.[17]

See also[edit]


  1. ^ Threat Levels Archived 11 June 2007 at the Wayback Machine, July 2006
  2. ^ "UK terrorism threat downgraded to 'substantial'". 4 November 2019. Retrieved 4 November 2019.
  3. ^ "Terror threat lowered after Tube bombing". BBC News. 17 September 2017. Retrieved 22 September 2017.
  4. ^ "Parsons Green: UK terror threat increased to critical after Tube bomb". BBC News. UK. 15 September 2017. Retrieved 15 September 2017.
  5. ^ Dodd, Vikram; Halliday, Josh; Pidd, Helen; agencies (27 May 2017). "Manchester attack: UK terror threat level reduced to severe". The Guardian. ISSN 0261-3077. Retrieved 22 September 2017.
  6. ^ "UK threat level raised to highest level". BBC News. 23 May 2017. Retrieved 23 May 2017.
  7. ^
  8. ^
  9. ^
  10. ^ "Irish terror attack a 'strong possibility'". BBC News. 25 September 2010. Retrieved 20 December 2010.
  11. ^ "Press Release: Increased risk of Irish-related terrorism". United Kingdom Home Office. 24 September 2010. Retrieved 20 December 2010.
  12. ^ Bunkall, Alistair (4 June 2016). "Was it a mistake to lower the UK terror threat before London Bridge attack?". Sky News. Retrieved 4 June 2016.
  13. ^ a b c "Threat levels". MI5. Retrieved 1 April 2017.
  14. ^ Foley, Frank (2013). Countering Terrorism in Britain and France: Institutions, Norms and the Shadow of the Past. Cambridge University Press. p. 166. ISBN 978-1-107-02969-9.
  15. ^ Hennessey, Thomas; Thomas, Claire (2011). Spooks the Unofficial History of MI5 From the First Atom Spy to 7/7 1945–2009. Amberley Publishing Limited. pp. 228–9. ISBN 978-1-4456-0801-3.
  16. ^ Staniforth, Andrew; Sampson, Fraser (2012). The Routledge Companion to UK Counter-Terrorism. Routledge. p. 276. ISBN 978-1-136-25430-7.
  17. ^ "UK terror threat level raised to critical, meaning an attack is imminent, Prime Minister says'". The Telegraph. 15 September 2017. Retrieved 15 September 2017.

External links[edit]