Terror threat still lingers
Updated on 20 July 2009
The terrorist threat level may have been lowered, but there is still a "strong possibility" of an attack. Jane Deith is at the MI5 building in central London.
The threat level, which is set by the Joint Terrorism Analysis Centre, has been reduced from severe to substantial, which means an attack is no longer "highly likely".
But Home Secretary Alan Johnson said the country still faces a "real and serious" threat from terrorists and urged members of the public to remain vigilant.
The Joint Terrorism Analysis Centre (JTAC), a unit in MI5, sets the level based on an analysis of intelligence. The assessment covers potential attacks by al-Qaida or linked extremist groups.
Five levels of threat
There are five levels of threat, ranging from low, meaning an attack is unlikely, to critical, when an attack is expected imminently.
Mr Johnson said: "The Joint Terrorism Analysis Centre has reduced the threat to the UK from international terrorism from Severe to Substantial.
"This means that an attack on the UK is a strong possibility. JTAC make their judgments based on a broad range of factors, including the intent and capabilities of international terrorist groups in the UK.
"We still face a real and serious threat from terrorists and the public will notice little difference in the security measures that are in place, and I urge the public to remain vigilant.
"The police and security services are continuing in their thorough efforts to discover, track and disrupt terrorist activity."
The shift means the threat level is now at its lowest since May 2005 when it was set at substantial, two months before the 7 July bombings.
At the time the threat was rated under a slightly different system and not made public. The threat level was first made public on 1 August 2006, when it was set at severe.
It was raised to critical on 10 August that year after a series of arrests over an alleged plot to blow up transatlantic aircraft, but lowered to severe again the following week.
The threat level was last at critical in June 2007, following the attack on Glasgow airport and the failed car bombings in central London.
The level is under constant review and can change quickly in response to events. Earlier this month, the country's most senior counter-terrorism officer, John Yates, hinted at the possibility of a change.
He told the Association of Chief Police Officers' conference in Manchester: "I think there is a possibility the threat level may come down.
"It is logical because we cannot keep having it high unless the threat is there."
The threat from dissident Republican and Loyalist terrorists in Northern Ireland is assessed separately.
