"Just Stop Oil supporters in prison are political prisoners," the group claimed, as two days of hearings began at London's Court of Appeal, closely watched amid fears that peaceful protest is being stifled in the UK.

"They are not there because they disrupted or harmed everyday people... No, they are there because Just Stop Oil threatens the profits of the fossil fuel industry," added the group, which has launched high profile protests since being formed in 2022 to fight the use of fossil fuels.

Sixteen activists, including some who threw tomato soup on a Vincent van Gogh's "Sunflowers" painting at London's National Gallery, are seeking to reduce or quash sentences imposed for four separate protests.

Outside court, dozens of supporters held up banners calling "Protect the right to protest" and "Free political prisoners". Others sat on the ground holding photos of those in jail.

Two activists accused of throwing orange paint powder on the megalithic standing stones at Stonehenge last year were to appear Wednesday at Salisbury Crown Court, in western England.

They face charges of damaging an ancient protected monument and intentionally or recklessly causing a public nuisance.

In the London court, five others are appealing jail terms imposed after being convicted of conspiracy to cause public nuisance when planning to blockade a motorway during an online call.

The group received prison terms of between 15 months and five years -- thought to be the longest sentences ever imposed for non-violent protest in the UK.

Environmental NGOs Greenpeace and Friends of the Earth have joined what they call "a critically important legal appeal over the right to protest".

"These sentences are much longer than any other peaceful protest-related defence in history," maintained Katie de Kauwe, Friends of the Earth lawyer.

- 'Crossing the line' -

On Thursday, a coalition of climate and pro-Palestinian organisations plans to mobilise hundreds of people to block the road outside the appeal court in support of the activists.

Climate protests have not stopped despite the jail terms.

On Tuesday, police arrested two Just Stop Oil activists for disrupting a London staging of Shakespeare's "The Tempest" starring Hollywood actor Sigourney Weaver.

And on Wednesday, a group from Extinction Rebellion interrupted a London conference of insurance companies.

The activist stunts have drawn condemnation from politicians and police and sparked a backlash among some sections of the public.

In July, five of the 16 activists who have brought the appeal were stunned after being sentenced to between four and five years in prison for planning to block the M25 motorway around London.

They include Roger Hallam, 58, one of the co-founders of JSO and Extinction Rebellion, another direct action environmental protest group. His four co-accused were also jailed.

"The plain fact is that each of you some time ago has crossed the line from concerned campaigner to fanatic," judge Christopher Hehir said during sentencing.

- 'Dark day' -

The length of the prison terms shocked NGOs and environmental campaigners.

The UN Special Rapporteur for Environmental Defenders, Michel Forst, called it "a dark day for peaceful environmental protest and indeed anyone concerned with the exercise of their fundamental freedoms" in Britain.

Greenpeace and Friends of the Earth said the sentences "could have far-reaching implications for the future of peaceful protest".

CIVICUS, a global alliance of civil society organisations and activists, has said civil freedoms are being "obstructed" in the UK.

The country's previous Conservative government adopted an increasingly hostile stance towards disruptive direct action to protest environmental policy.

Ministers passed a series of laws toughening punishments for such offences.

cla/har/jkb

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