The Prime Minister has branded protesters who have blocked major UK roads as “irresponsible crusties” as tougher powers to tackle them were outlined.

Boris Johnson said Insulate Britain protesters, who have blocked highways across the South East in recent weeks, have been “doing considerable damage to the economy”.

His comments came ahed of Home Secretary Priti Patel confirming plans for new measures against the likes of Insulate Britain and Extinction Rebellion in her conference speech.

Ms Patel said she wants to increase the maximum penalties for disrupting a motorway while also criminalising interference with major roads, railways and the press.

Mr Johnson told LBC: “There are some people who call those individuals legitimate protesters.

“They are not. I think they are irresponsible crusties who are basically trying to stop people going about their day’s work and doing considerable damage to the economy.

“That is why we have taken the powers and why Priti Patel is doing the right thing to bring in powers so they can get six months or an unlimited fine.”

Protesters from Insulate Britain have blocked major roads including the M25 and the M4 in recent weeks.

A court injunction was taken out to prevent their blockade of the M25, but demonstrations have continued, most recently on roads across London on Monday.

Ms Patel, speaking at the Conservative Party conference in Manchester, told party members: “It is because of our commitment to putting the needs of the hard-working, often silent, majority first that I will not tolerate so called eco-warriors trampling over our way of life and draining police resources.

“Their actions over recent weeks have amounted to some of the most self-defeating ‘environmental’ protests this country has ever seen. Freedom to protest is a fundamental right our party will forever fight to uphold. But it must be within the law.

“Measures already going through Parliament will ensure these criminals can be brought to justice for the disruption they are causing.

“But we are going further to close down the legal loopholes exploited by these offenders.

“So, today, I can announce I will also increase the maximum penalties for disrupting a motorway, criminalise interference with key infrastructure such as roads, railways and our free press, and give the police and courts new powers to deal with the small minority of offenders intent on travelling around the country, causing disruption and misery across our communities.”