What the threat levels mean

Threat levels are designed to give a broad indication of the likelihood of a terrorist attack.

  • LOW means an attack is highly unlikely
  • MODERATE means an attack is possible, but not likely
  • SUBSTANTIAL means an attack is likely
  • SEVERE means an attack is highly likely
  • CRITICAL means an attack is highly likely in the near future

How are threat levels decided?

The threat level for the UK from international terrorism is set by the Joint Terrorism Analysis Centre (JTAC).

MI5 is responsible for setting the threat levels from Irish and other domestic terrorism both in Northern Ireland and in Great Britain.

In reaching a judgement on the appropriate threat level in any given circumstance several factors need to be taken into account.

These include:

  • Available intelligence. It is rare that specific threat information is available and can be relied upon. More often, judgements about the threat will be based on a wide range of information, which is often fragmentary, including the level and nature of current terrorist activity, comparison with events in other countries and previous attacks. Intelligence is only ever likely to reveal part of the picture.
  • Terrorist capability. An examination of what is known about the capabilities of the terrorists in question and the method they may use based on previous attacks or from intelligence. This would also analyse the potential scale of the attack.
  • Terrorist intentions. Using intelligence and publicly available information to examine the overall aims of the terrorists and the ways they may achieve them including what sort of targets they would consider attacking.
  • Timescale. The threat level expresses the likelihood of an attack in the near term. We know from past incidents that some attacks take years to plan, while others are put together more quickly. In the absence of specific intelligence, a judgement will need to be made about how close an attack might be to fruition. Threat levels do not have any set expiry date, but are regularly subject to review in order to ensure that they remain current.

Threat level history

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.

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.

Date National Threat Level Northern Ireland-related Threat Level to Northern Ireland
23 July 2019 SEVERE SEVERE

Threat levels prior to July 2019

Date Threat from international terrorism Threat from Northern Ireland-related terrorism
in Northern Ireland in Great Britain
1 March 2018 SEVERE SEVERE MODERATE
17 September 2017 SEVERE SEVERE SUBSTANTIAL
15 September 2017 CRITICAL SEVERE SUBSTANTIAL
27 May 2017 SEVERE SEVERE SUBSTANTIAL
23 May 2017 CRITICAL SEVERE SUBSTANTIAL
11 May 2016 SEVERE SEVERE SUBSTANTIAL
29 August 2014 SEVERE SEVERE MODERATE
24 October 2012 SUBSTANTIAL SEVERE MODERATE
11 July 2011 SUBSTANTIAL SEVERE SUBSTANTIAL
24 September 2010 SEVERE SEVERE
(first published)
SUBSTANTIAL
(first published)