Roadblocks will surround this year’s Notting Hill Carnival and armed police in plain clothes will mix with the crowds to guard against an anticipated terror attack.

The street party attracts around 1,000,000 people every year, and other large-scale public events, including the Leeds and Reading music festivals, will have extra protection.

Security forces do not have specific intelligence on the events, but the terror threat remains at “severe” and festivals are thought to venerable after the spate of attack across Europe.

Islamists killed 15 people in car and van attacks in Barcelona last week, and other public gatherings, such as Bastille Day celebrations in France and a Christmas market in Berlin, have been hit.

One report quoted a security source as saying that armed troops would mingle with the public at sites considered most at-risk. The source told the Mail on Sunday:

“They will be casually dressed with their weapons hidden beneath their clothes. They won’t be in traditional military vehicles, either.

Roadblocks in London to stop vehicle attacks. Credit: Breitbart London/Rachel Megawhat

“Recently a company of Special Forces Support Group troops completed a live firing exercise using civilian armoured vehicles and they will be called upon… the other troops who have been called up for the bank holiday weekend include personnel from the Special Reconnaissance Regiment.”

A spokesman for the Metropolitan Police declined to comment on reports that there would be vehicle barriers for the first time at the Notting Hill Carnival in west London, which usually attracts about one million people.

“You factor what’s happening in your patch and elsewhere into your policing policy. There may be something that comes out a bit nearer the time. It will have a policing plan in place as we do every year,” the spokesman said.

Vehicle barriers have already been used to protect the Edinburgh festival and London’s gay pride celebrations. Police called the concrete barriers “hostile vehicle mitigation” and also deployed more uniformed officers and “a search and accreditation regime.”

Numerous other festivals contacted by The Times also confirmed they will beef up security this year.

They include the Greenbelt Festival of arts and music in Northamptonshire, the Medieval Festival in East Sussex, Creamfields, a dance music event in Cheshire, Insomnia, Britain’s largest gaming festival, Carfest South in Hampshire, Edinburgh Mela, and Manchester Pride.