The Joint Terrorism Analysis Centre (JTAC) is an all-source intelligence organisation closely related to the United Kingdom Security Service which provides advice to the British government and firms within the Critical National Infrastructure on terrorist threats.

This article relies excessively on references to primary sources. (June 2016)

Operating from Thames House on Millbank in central London, it provides regular assessments to government departments, major companies and institutions, predominantly in the transport, financial services, utilities and telecommunications industries.

The Director of JTAC reports to the Director General of the Security Service (commonly known as MI5), and directs a staff including personnel from the Security Service, Secret Intelligence Service (commonly known as MI6), Government Communications Headquarters (GCHQ), Defence Intelligence Staff, Counter Terrorism Policing and a further six government departments.^[which?] Personnel are seconded to JTAC but remain under the authority of their parent organisations.

As a body closely related to the Security Service, JTAC is bound by the provisions of the Intelligence Services Act 1994 and is subject to the oversight of the Intelligence and Security Committee.

Assessments are used to inform the threat levels disseminated through the Security Service, Home Office and Ministry of Defence. Until very recently these threat levels were promulgated in a form known as the BIKINI state and Tesseral State. The current threat system is similar to, and largely aligned with, the US Department of Homeland Security rating system.

The range of five available threat levels is:

• Low – an attack is unlikely
• Moderate – an attack is possible, but not likely
• Substantial – an attack is likely
• Severe – an attack is highly likely
• Critical – an attack is highly likely in the near future

This is a reduction from the previous seven levels in order to simplify communication to the general public.

JTAC rose to public prominence following the terrorist attacks in London in July 2005. Media reporting highlighted a reduction in the threat level from "Severe General" to "Substantial" based on the assessment that the risk of an attack was at its lowest point since 9/11. These news reports were the first release of threat gradings outside the Critical National Infrastructure.

• British intelligence agencies
• Counter-terrorism
• Threat level (disambiguation)
• National Counterterrorism Center (NCTC) – a similar body in the United States

• "Report into the London Terrorist Attacks on 7 July 2005" (PDF). UK Intelligence and Security Committee. May 2006. Archived from the original (PDF) on 4 June 2006. (pdf)

• The UK's Threat Level System, MI5 website
• Current threat level, Home Office website
• Joint Terrorism Analysis Centre, MI5 website