Environmental activists who blocked the M25 have vowed to continue their campaign after National Highways was granted an injunction against their protests.

The campaign group Insulate Britain, which has shut down parts of the M25 five times in just over a week, said “our campaign will go on” despite the threat of jail, or pre-emptive arrests from the police.

At least 270 people have been arrested following five protests on the motorway around Greater London this week.

On Wednesday, the government successfully applied to the high court for an order which prohibits anyone from blocking the M25.

Anyone who breaks the injunction could be found to be in contempt of court, which carries a maximum penalty of two years in prison or an unlimited fine.

Outside the Home Office in central London, about 50 protesters from the group said they would continue to block roads until the government pledges to properly insulate UK homes.

Louise Lancaster, a teacher and supporter, said: “I will continue to sit in the road until the government insulates Britain.”

Earlier, the transport secretary, Grant 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.”

An 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 had 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 on to the road before they were dragged away by officers.

The Home Office minister Kit Malthouse confirmed that National Highways had secured an interim injunction to prevent protesters from occupying the M25, adding that efforts are ongoing to secure a “full injunction later this week”.

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.

The protest group has been calling for the installation of heat-saving measures in social housing by 2025, and all homes by 2030.

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.

Making a statement to the Commons, Malthouse said: “We do not change policies or make policies in this country though mob rule or being held to ransom, and these people should not suppose for one moment that the public is with them.”

Shadow Home Office minister Holly Lynch said the right to protest was a “fundamental freedom, a hard-won democratic tradition”, but that Labour “backed the police” if protests were unsafe or illegal.