Lawyer Danny Friedman told London's Court of Appeal in January that the prison terms of between 15 months to five years for separate protests were "the highest of their kind in modern British history".

The activists "did what they did out of sacrifice" and were acting in the "best interests of the public, the planet and future generations," he said, asking for the jail terms to be reduced.

Prosecutors argued the sentences had been merited as "all of these applicants went so far beyond what was reasonable".

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

Lady Chief Justice Sue Carr is to hand down the ruling at the Court of Appeal in London at 1000 GMT on Friday, in a case which could have far-reaching implications for future protests.

The hearing is being closely watched amid fears that peaceful protest risks being stifled in Britain.

Activist groups Just Stop Oil (JSO) and Extinction Rebellion have launched high profile protests in recent years to fight the use of fossil fuels, which scientists say are causing global warming and climate change.

- Tomato soup, orange powder -

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.

The 16 activists, including some who threw tomato soup on Vincent van Gogh's "Sunflowers" painting at London's National Gallery, are seeking to reduce or quash lengthy jail terms.

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

Other cases are still before the courts, including charges brought against two Just Stop Oil members accused of throwing orange paint powder over the stone megaliths of Stonehenge as well as two activists charged with spray-painting the tomb of naturalist Charles Darwin in Westminister Abbey.

The activists' 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 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, a key transport link for the capital.

They include Roger Hallam, 58, a co-founder of JSO and Extinction Rebellion. 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 their sentencing.

The country's previous Conservative government took a hostile stance towards disruptive direct action, and passed laws toughening punishments for such offences.