A silent protest was held outside the Russian embassy in London and a petition was handed in demanding the immediate release of video journalist Kieron Bryan.
Mr Bryan, from Peckham, London, was among 30 people arrested after Russian security forces boarded a Greenpeace ship on 18 September.
The 29-year-old has been charged with hooliganism.
His brother Russell said Kieron was "confused and angry".
Kieron, originally from Devon, is one of six Britons being held in a prison in Murmansk.
Speaking to BBC News, his brother said: "We feel and he feels that he shouldn't be there, he's a freelance journalist not a Greenpeace activist.
"He goes through some positive moments when he hears from family and friends through letters and he also has his dark times. He spends 23 hours in a cell presumably on his own.
"It's scary for all of us, it's terrifying."
Journalists and supporters of the Free Kieron campaign held a silent protest outside the Russian embassy, in Gee Street.
The National Union of Journalists(NUJ), which helped to organise the campaign, said the situation was "unacceptable".
An NUJ spokesman said: "After first being charged with piracy, he's now facing trial for hooliganism. This is unacceptable. He's facing up to seven years in jail for simply doing his job. He must be freed immediately.
"It is absolutely vital that the Russians understand that Kieron is a freelance journalist, not an activist."
A petition signed by 1,400 journalists, including national newspaper editors, calling for his release was given to staff at the Russian embassy.
Those taking part in the protest covered their mouths with tape while the protest was held.
On Monday the Netherlands took the case of the Dutch-flagged ship and its crew to the UN tribunal based in Hamburg which adjudicates on disputes arising out of the UN Convention on the Law of the Sea.
Earlier, the Russian foreign ministry released a statement pointing out that Moscow had opted out of UN Law of the Sea dispute procedures in 1997.
The Foreign and Commonwealth Office said it was providing consular assistance to those held and were in touch with Russian authorities but couldn't release any details regarding the legal situation in Russia.