Environmental activists blocking the M25 face possible imprisonment after National Highways was granted an injunction against their protests, the transport secretary, Grant Shapps, has said.

The campaign group Insulate Britain has shut down parts of the M25 five times in just over a week.

Shapps wrote on Twitter: “Invading a motorway is reckless and puts lives at risk. I asked National Highways to seek an injunction against M25 protesters which a judge granted last night. Effective later today, activists will face contempt of court with possible imprisonment if they flout.”

The application for an injunction was lodged at the high court on Wednesday, after Shapps and the home secretary, Priti Patel, wrote an article vowing to ensure “guerrilla” activists “cannot keep disrupting and endangering people’s lives”.

They said the police had their support to take “decisive action” against any future demonstrations that they say are disruptive.

Insulate Britain said there have been 338 arrests of its protesters, with its last action on Tuesday blocking the M25 in both directions. Its key demand is for the government to do more to insulate Britain’s homes, starting with those of the poorest.

Footage taken by LBC at the protest on Thursday appeared to show people walking on to the motorway and sitting down on the ground in front of moving traffic. Some held up banners reading “Insulate Britain” and poured blue paint onto the road before they were dragged away by officers.

In a column for the Daily Mail, Shapps and Patel said: “[The protesters] have broken the law, undermined the cause they believe in, alienated the public and created extra pollution, in one of the most self-defeating environmental protests this country has ever seen.

“We are giving [police] powers to better manage such guerrilla tactics in future. In the medium term, the police, crime, sentencing and courts bill will put public nuisance on a statutory footing, ensuring there are appropriate sentences for the harm caused.”

Insulate Britain said new people had joined its campaign to improve home insulation in addition to others who have been involved in similar demonstrations in Hertfordshire, Kent, Essex and Surrey over the past two weeks.

It said the recent rise in gas and electricity costs had “increased the urgency” for change and it would end its campaign as soon as it hears a “meaningful commitment” in response to its demands.