UK’s national terrorism threat level has been raised to “severe” following the murderous attacks by Islamist militants in France and Austria.

The Joint Terrorism Analysis Centre (JTAC) made the assessment following a spate of attacks in France and a shooting rampage by an Isis supporter in Vienna.

Priti Patel, the home secretary, said: “This is a precautionary measure and is not based on any specific threat.

“The public should continue to remain vigilant and report any suspicious activity to the police.”

Isis, al-Qaeda and other jihadist groups have been ramping up calls for supporters to launch atrocities around the world in recent days.

The terror threat level was lowered to substantial a year ago, just weeks before an Islamist extremist murdered two people at a rehabilitation event in London.

It was followed by three other alleged terror attacks this year in HMP Whitemoor prison, Streatham and Reading.