The British Home Secretary Alan Johnson says, Britain's terror threat level is being raised from "substantial" to "severe". The new alert level means a terrorist attack is considered "highly likely". It had stood at substantial since July. It is in response to the perceived increased threat from international terrorism following the failed Detroit airliner bombing on Christmas Day. Mr Johnson stressed there was no intelligence to suggest a terrorist attack was imminent. The decision to raise the threat level was made by the Britain's Joint Terrorism Analysis Centre (JTAC). Mr Johnson said JTAC kept the threat level under constant review, making its judgments based on a broad range of factors, including the intent and capabilities of international terrorist groups in Britain and overseas.