Prime Minister Boris Johnson has branded eco-extremist group Insulate Britain “irresponsible crusties” for blocking roads in protest over climate change.

Over the past three weeks, members of the Extinction Rebellion offshoot have blocked major motorways in the UK including the M25, demanding the mass and expensive retrofit of British houses to make them more environmentally friendly.

The group has provoked the ire of members of the public, who have criticised them for blocking ambulances and those trying to get their loved ones to hospital, as well as holding up people on their way to work or to take their children to school.

Prime Minister Johnson referred to Insulate Britain as “crusties” on LBC on Tuesday, a term associated in recent years with environmentalists too busy protesting to bath regularly.

Mr Johnson told Nick Ferrari on Tuesday: “There are some people who call those individuals legitimate protesters. They’re not. I think they’re irresponsible crusties who are basically trying to stop people going about their day’s work and doing considerable damage to the economy.

“That’s why we’ve taken the powers and why Priti Patel is doing the right thing to bring in powers so that they get six months or a limited fine.”

However, name-calling from the articulate and humourous prime minister has done little in the past to stop other protesters in their tracks, with Extinction Rebellion still actively demonstrating in London on a regular occurrence, despite Mr Johnson branding them “uncooperative crusties” in 2019.

Injunctions on protests on the M25 also appear to not be effective, with Insulate Britain activists having continued to block the major ring road around London, and launching more protests on other major routes and junctions across the country.

Prime Minister Johnson has also appeared in recent years to have embraced the crustier side of life himself, after committing the UK to banning the sale of new petrol cars as well as frequently espousing the progressive, green Build Back Better mantra.

The remarks may have prompted Insulate Britain to apologise for the inconvenience, but the group said it was going to carry on with the protesting, saying that unless the government submits to their demands, “these inconveniences will continue”.

On Tuesday, the Royal Courts of Justice served more than 100 Insulate Britain protesters with injunctions against protests that block roads.

Home Secretary Priti Patel also announced plans to increase the maximum penalty for road-blocking protests. The government will also look to criminalise interference with major British infrastructures, such as roads and railways.

Public anger over the protests came to a head on Monday, with footage shared widely on social media showing angry members of the public and ambulance workers pulling protesters off the road in an attempt to let an ambulance through.

Former Brexit Secretary David Davis told talkRADIO’s Julia Hartley-Brewer on Tuesday: “I am one of the strongest defenders in the House of Commons on the right to demonstrate… but the right to demonstrate is not the right to inconvenience.”

“If you set out to wreck people’s lives, if you set out to stop them getting to work or a hospital appointment” then that is not legitimate protest, Mr Davis said.

Latest polling revealed that 53 per cent of Britons have unfavourable views of Insulate Britain, including 36 per cent who have a “very unfavourable” view of the group. Just 16 per cent said they had a favourable view of the eco-extremists.