Human rights campaigner Peter Tatchell has announced he is standing down as a Green Party candidate for Oxford East.

In a statement, the veteran gay activist said that brain injuries sustained in Moscow and Brussels meant he could not campaign effectively for the seat.

In 2001, he was badly beaten by Zimbabwe’s leader Robert Mugabe’s bodyguards while attempting to perform a citizen’s arrest on him for torture charges.

He was also hurt in 2007 by neo-Nazis during Moscow Pride.

Tatchel said these injuries were compounded by an accident in July, when he hit his head on a metal handrail while on a bus.

He said: “It would not be right for me to seek election if I could not do the job of an MP to the high standards that I want and that Oxford East voters have a right to expect.

“If I was elected, I could manage the parliamentary duties or the constituency work. But my health is not strong enough for me to do both.

“The injuries don’t stop me from campaigning but I am slower, make more mistakes, get tired easily and take longer to do things. My memory, concentration, balance and coordination have been adversely affected. I can’t campaign at the pace I used to.”

But he added: “I don’t regret a thing. . . My beatings had the positive effect of helping draw international attention to the violent, repressive nature of the Russian and Zimbabwean regimes. I’m glad of that.”

Tatchell said he was disappointed but thanked the Green Party for its “immense kindness, support, and generosity”.

He said he had been told by doctors he could see some improvement in his health after a year if he slows down but said it was “unlikely” he would fully recover.

Sid Phelps, chair of Oxfordshire’s Green Party, told PinkNews.co.uk: “We’re sad about this, it’s a real shame. He’s almost a martyr to the green and human rights causes. It’s a real shame but what can you do? People’s health must come first. He’s got hurt due to political activity really.

“He’ll be a loss but I’m sure he’ll be writing and campaigning wherever he can.”

Oxfordshire Greens plan to select a new candidate in January.

Russian gay rights campaigner and organiser of Moscow Pride Nikolai Alekseev, also paid tribute to Tatchell’s work.

He said: “Of course, it’s a sad news and we all send our best wishes to Peter from Moscow, hoping he can soon recover and get back to his usual working capacities.

“Peter has been a strong supporter of our cause in Russia since day one. His words of support always materialised in his physical presence in all our events. He only missed one as his doctor did not want him to travel in 2008 when he was already suffering from the 2007 beating.

“Having the chance to be closely in contact with him since 2005 only made me confident in the high opinion I had before of his campaigns and achievements. There is no secret if I say that outsde the LGBT community he is one of the few gay activists recognised by straight people.”