The public is being urged to turn detective and report terror suspects to police in the final days before Christmas.
Tip-offs have gone up by 50% in the past year but police say they still need help to spot potential terrorists who might threaten big festive crowds.
Christmas markets, shopping centres, concerts and pantos across the UK are all vulnerable to attack, said counter-terror police chief Jon Savell.
“The public are our eyes and ears,” said Deputy Assistant Commissioner Savell. “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.”
DAC Savell toured a bustling Christmas market in south London with security minister Dan Jarvis, urging stall-holders and shoppers to be alert, but not alarmed.
Unlike Germany and France, the UK has no history of Christmas terror attacks, nor have investigators disrupted any Christmas-time plots, but with uncertainty over recent regime change in Syria, and ongoing Middle East conflicts, counter-terror police are as busy as ever.
They are currently involved in 800 investigations and have thousands of possible suspects on their radar.
There were 52 more arrests for terrorism offences last year than in 2022 – an increase of 31% and the highest number in a single year since 2019.
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Crime correspondent Martin Brunt speaks with Deputy Assistant Commissioner Savell
‘Heightened vigilance’ over Christmas period
Mr 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.”
Police and security guards mix up tactics
DAC Savell said one of the measures to counter threats was to mix up security tactics.
“There are plenty of police officers and security guards and they are being unpredictable in what they do and I think that’s a really key message for people who might be intent on harm, you never actually know if police and security will be there,” he said.
And, of course, there are less obvious security measures – intelligence reports, technology and surveillance, the things police don’t like to talk about.
The current official terror threat level is mid-range at “substantial”, meaning an attack is likely at any time.