Public urged to look out for potential terrorists at pantos and Christmas markets

People have been told to be 'vigilant'

In particular, police have said they need help at events with big crowds such as festive markets, concerts and pantos.

Counter-terror police chief Jon Savell said these sort of events across the UK were particularly vulnerable to attack.

Deputy Assistant Commissioner Savell said: "The public are our eyes and ears. Without public support and vigilance, it actually makes our job an awful lot more difficult.

"Our concern is public spaces, crowded places and the natural vulnerability of that for obvious reasons, places where you've got many, many people, tourists, shoppers, local residents and people coming to work.

"What we want to do is make sure we get messages across for members of the public to be vigilant."

Savell and security minister Dan Jarvis went to a Christmas market in south London to urge stall-holders and shoppers to be alert, but not alarmed, Sky News reports.

Over the last year, tip-offs to police have gone up by 50 per cent, and counter-terror police are currently involved in 800 investigations and are monitoring thousands of possible terror suspects.

There has never been a Christmas terror attack in the UK, but the current official terror threat level is mid-range at "substantial." This means an attack is likely at any time.

Jarvis said: "It is my job as the security minister to be permanently concerned about the nature of the risks, the threat we face as a country, but yes as we move into the Christmas period clearly there needs to be a heightened vigilance around events that lots of people are going to attend.

"The public are very sensible; they will take a judgment based on their intuition as to whether something that they see is unusual or not.

"If you have any concerns about the activity you see, whatever it might be, then please do flag that with the police, and then they can take a decision about how best to proceed and respond to it."