London Telegraph 
Monday, July 20, 2009
The threat of a terrorist attack in Britain has reduced from “severe” to “substantial” for the first time since the bombings of July 2005.
It is the third of five threat levels and means the Joint Terrorism Analysis Centre, a unit within MI5, believes that the danger of an attack is now “highly likely” rather than a “strong possibility”.
The assessment is based on a range of factors including intelligence, current terrorist activity, comparison with events in other countries and previous attacks.
Alan Johnson, the Home Secretary said: “”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.