The activists with the Just Stop Oil (JSO) group last year received prison terms of between 15 months and five years for several stunts, including throwing soup on Vincent van Gogh's "Sunflowers" in London and blocking the M25 motorway around the UK capital.

They have appealed the length of their sentences, but prosecutors told the court on Thursday that "each of the judges were right" as "all of these applicants went so far beyond what was reasonable".

Their actions also presented an "extreme danger" to the public, they said.

The five "conspirators" who organised the action in which activists climbed onto multiple gantries over the M25 motorway, leading to its closure, "were at the pinnacle of the organisational pyramid of what was intended to be the 'biggest disruption in British modern history'," the court heard.

The action affected around 700,000 vehicles over four days, and the five activists were sentenced to jail terms of between four and five years.

The sentences were "the highest of their kind in modern British history", Danny Friedman, a lawyer for the activists, told the court on Wednesday.

Hundreds of JSO supporters gathered outside the central London court on Thursday, sitting in silence on the road with portraits of around 100 people they said were "political prisoners" jailed across the world for environmental activism.

"We know that the UK has become one of the most difficult places to protest anywhere in the world," broadcaster and campaigner Chris Packham told AFP.

"We must fight fiercely for the right to stand up and protest and make sure our leaders take action, far more urgently, to address this critical issue" of climate change, he added.

Police watched on, but the protest dispersed peacefully.

Just Stop Oil, which is urging the government to ban fossil fuel use by 2030, is known for its eye-catching stunts at museums, sports events and shows but has attracted criticism over its methods.

In recent years, previous Conservative governments passed a series of laws to punish their actions more severely.

NGOs Greenpeace and Friends of the Earth have denounced the crackdown and have joined the appeal trial, which they say will have significant implications for the future of peaceful protest.

The court will publish its decision at a later date.