How the UK's terror threat levels work

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

The UK's national threat level has been moved up to severe following a terror attack that saw two Jewish men stabbed in north London.

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There are five different threat levels, with the Joint Terrorism Analysis Centre (JTAC) responsible for deciding at which level the UK should sit.

The five terror threat levels are:

• Low - an attack is highly unlikely

• Moderate - an attack is possible, but not likely

• Substantial - an attack is likely

• Severe - an attack is highly likely - this is the UK's current level

• Critical - an attack is highly likely in the near future

JTAC is based at MI5's headquarters in London and is comprised of representatives from 16 government departments and agencies.

It brings together counter-terror experts from the police, government and security agencies.

JTAC also works especially closely with MI5's international counter-terrorism branch, which manages investigations into terrorist activity in the UK.

In deciding on the UK's threat level, JTAC considers:

• The level and nature of current terrorist activity, in comparison with events in other countries and previous attacks.

• What is known about the capabilities of the terrorists in question and the method they may use based on previous attacks or from intelligence.

• The overall aims of the terrorists and the ways they may achieve them including what sort of targets they would consider attacking.

• How close an attack might be to fruition.

How has the threat level changed over the years?

The system was first made public in 2006 and, since then, it has most often been at the severe level, and not been lower than substantial.

The critical level has been in place four times: in August 2006, after a plot to detonate explosives on transatlantic flights; in June 2007, after an attempted car bomb attack at Glasgow airport; and in May and September 2017, after the Manchester Arena bombing and the Parsons Green District line attack, respectively.

It was downgraded to severe a few days after the Parsons Green incident and remained there until being lowered to substantial in November 2019.

The last time the level was raised to severe was in November 2021 after two incidents in the space of a month, the murder of Conservative MP Sir David Amess in October and a car explosion outside a Liverpool hospital on Remembrance Sunday.

It was downgraded back to substantial in February 2022.

(c) Sky News 2026: How the UK's terror threat levels work