Via Times Online:
Britain’s terrorist threat level was raised tonight from â€œsubstantialâ€ to â€œsevereâ€ – meaning that counter-terrorism agencies believe an attack is â€œhighly likelyâ€.
The measure was approved at a meeting of the Governmentâ€™s Cobra emergency committee and announced by Alan Johnson, the Home Secretary.
The Times understands that the decision to raise the threat level is connected to the conference on Afghanistan taking place at Lancaster House, London, next Thursday.
Sources said there had been intensive discussions throughout the day relating to intelligence suggesting a possible attempted â€œspectacularâ€ by an al-Qaeda affiliated group.
But the shift was also described by one source as â€œprecautionaryâ€ rather than rooted in any firm information that an identified terror cell was plotting an attack.