Greenpeace protesters have gathered at petrol stations across the country to plead for the release of 28 activists and two journalists from a prison in Russia.
The so-called Arctic 30 were arrested after protesting at an oil rig in Russia in September and now face charges of piracy, a crime that carries notoriously harsh sentences.
Greenpeace is today targeting Shell outlets in the UK following reports that the company is to join with Russian oil giant Gazprom in drilling off the Arctic shore.
It comes as Russian officials have signalled they will ask that the Greenpeace group be detained an extra 3 months - meaning they could be behind bars over Christmas.
Two journalists and 28 Greenpeace activists are being held in St Petersburg charged with piracy and hooliganism after Russian authorities seized the Arctic Sunrise vessel in September.
Today, activists will be asking members of the public to show their support for the 30 - six of whom are UK nationals - by sending a message to the Russian Embassy in London asking for their release, Greenpeace said.
Protesters will also be asking for signatures on a petition asking the fuel giant to pull out of its "risky and reckless joint venture with Gazprom to drill for oil in the Arctic Ocean".
In a letter handed out by activists to managers at each Shell station, John Sauven, executive director of Greenpeace UK, wrote: "28 activists and two journalists remain in detention after the seizure of our ship Arctic Sunrise by armed Russian Federal Security Bureau agents.
"(They) now face exceptionally serious charges of hooliganism and piracy, accusations with no merit in either Russian or international law.
"Greenpeace believes that the extraction of oil and gas resources of the Arctic is incompatible with catastrophic climate change. Perhaps more pertinently for Shell, however, is that your new partnership with Gazprom could well become a corporate millstone."
More than 30 protesters have met outside a petrol station in central London.
Abby Mortimer, 26, co-ordinator of Greenpeace's south west contingent, said the group would picket three Shell spots around London.
She said: "We have obviously been protesting against Shell for a while. Shell are considering going into partnership with Gazprom. They have a dreadful environmental record and were key in the locking up of 30 of our volunteers; they asked for the peaceful volunteers to be arrested.
"We are here to say that Shell need to abandon that partnership and to tell Gazprom that they need to release the Arctic 30."
Lauren Tobia, 31, a children's book illustrator, paid tribute to Frank Heweston, one of the 30 people believed to be detained in St Petersburg.
She said: "I'm absolutely disgusted and frightened for the Arctic 30. I know some of these people personally and I just need them to come home. They are stuck up there and all they have done is stick up for everybody; for their children and the planet."
She said of her colleague, a father of two: "He's a great guy. He's just a normal bloke like everybody else, an incredible bloke who goes the extra mile. I cannot speak eloquently because I'm so worried about him. I just hope that somehow we get more attention."
A spokesman for Shell said: "Our view is that any individual organisation has the right to protest as long as that protest is peaceful and safe and does not interfere with our staff or our customers. We have not had any reports of anything like that so far.
"We will not comment on the reasons for their protests."
Thousands of protesters across the UK have demonstrated in outrage since the charges were made