Just Stop Oil co-founder Roger Hallam has had his sentence reduced by a year after a High Court appeal.
He was among a group of 16 activists who challenged jail terms of between 15 months and five years for their roles in four demonstrations between August and November 2022.
Ten of them had their appeals dismissed.
Hallam was jailed for five years last July over a plot to disrupt M25 traffic, which saw 45 people climbing onto gantries over the motorway.
His sentence was reduced to four years on appeal.
Daniel Shaw, Louise Lancaster, Lucia Whittaker De Abreu, and Cressida Gethin each received four-year jail terms for their involvement in the same protest, which caused four days of disruption.
Shaw and Lancaster’s sentences were reduced to three years, while Whittaker De Abreu and Gethin’s sentences were reduced to 30 months.
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Gaie Delap, who was previously jailed for 20 months for her role in protests on the M25 had her sentence reduced to one of 18 months.
Her co-defendants, George Simonson, Theresa Higginson, Paul Bell and Paul Sousek, who were imprisoned for between two years and 20 months, had their appeals dismissed, along with six others involved in different protests.
They included Dr Larch Maxey, Chris Bennett, Samuel Johnson and Joe Howlett were jailed for between three years and 15 months after occupying tunnels dug under the road leading to the Navigator Oil Terminal in Thurrock, Essex.
The Court of Appeal also threw out challenges from Phoebe Plummer and Anna Holland were sentenced to two years and 20 months respectively after almost “destroying” Vincent van Gogh’s Sunflowers by throwing soup on its protective glass at London’s National Gallery.
Lawyers for the group of 16 told the court last month the sentences were “manifestly excessive”, breached the activists’ human rights, and should have taken into account their “conscientious motivation”.
The Crown Prosecution Service opposed the appeal, arguing “deterrence is required in order to protect the public”.
As the Lady Chief Justice Baroness Carr read out a summary of the Court of Appeal’s ruling, several campaigners in court stood and turned their backs, wearing T-shirts that read “Corruption in Court”.
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The sentences of Hallam and his four co-defendants were thought to have been the longest ever relating to peaceful protest.
During the trial at Southwark Crown Court, prosecutors alleged the M25 protests led to an economic cost of at least £765,000 while the cost to the Metropolitan Police was more than £1.1 million.
They also allegedly caused more than 50,000 hours of vehicle delay, affecting more than 700,000 vehicles, and left the M25 “compromised” for more than 120 hours.
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Raj Chada, head of criminal defence at law firm Hodge Jones & Allen, which represents the other protesters, said: “The small reduction in the case of Roger Hallam recognises the extraordinarily excessive sentences that continue to be given out to protesters in England.
“It is, however, extremely disappointing that many of the other sentences were upheld.
“No country in Europe gives such draconian sentences for peaceful protests, proving we are out of kilter with the rest of the civilised world.
“We are reviewing the judgment and considering an appeal to the Supreme Court.”
