Terror level in UK raised to 'severe'

Alan Johnson, the home secretary, said there was no intelligence to suggest an attack was imminent.

The escalation reversed a decision in July to downgrade the likelihood of a terror attack from "severe" to "substantial".

Johnson said the change was not ­specifically linked to the increased threat from international terrorism following the failed Detroit plane bombing on Christmas Day or to any other incident.

He said the Joint Terrorism ­Analysis Centre (Jtac), a unit within MI5, had taken the ­decision based on a broad range of ­factors, ­including the intent and ­capabilities of international terrorist groups in the UK and overseas.

Johnson said: "We still face a real and serious threat to the UK from ­international terrorism, so I would urge the public to remain vigilant and carry on ­reporting ­suspicious events to the appropriate authorities, and to support the police and security services in their ­continuing efforts to discover, track and disrupt ­terrorist activity."

He said the public should be reassured by the UK's "very adept and very focused counter-terrorism" services.