Peter Tatchell has emphasised what he calls the game-changing decision of London Mayor Boris Johnson to support David Cameron’s equal marriage reform, which was resoundingly accepted at second reading by a large majority in the House of Commons on Tuesday.

In an interview to the London Evening Standard, the human rights campaigner spoke about his previous dealings with the mayor at Pride London in 2010. Mr Tatchell recalls the moment he asked Mr Johnson whether he would support equal marriage.

“[Boris] stumbled for a few seconds and then said ‘yes.’ And that was hugely important. With Boris Johnson supporting marriage equality, it was suddenly respectable in large sections of the Conservative Party.

“Boris’s backing for same-sex marriage was a game-changer,” Mr Tatchell told the Standard.

In the interview, Mr Tatchell discussed his invitation to a reception for influential Londoners at City Hall, a few days after the Pride event, he again pushed Mr Johnson on the issue, and thanked him for his “support” of equal marriage.

“And the entire audience burst into cheers and applause. That was really significant too,” Mr Tatchell said.

Mr Tatchell, who intensely lobbied the government over the issue of equal marriage, went on to say that he valued the Mayor of London’s support for equal marriage.

“He’s the second most influential Tory politician after Cameron. Not all Tories love Boris, but very many do,” he said.

Talking on his forty year career as a human rights activist, Mr Tatchell said he originally estimated it would take fifty years to achieve gay equality.

“When I first became aware of the vast array of anti-gay laws on the statute book, I resolved to dedicate a part of my life seeking their repeal,” he said. “I calculated that it would take 50 years to win gay equality. But it turns out I was a bit of a pessimist. Once we get same-sex marriage, that goal will have been achieved.”

Mr Tatchell said despite the importance of equal marriage for equality, he probably wouldn’t get married himself.

“Personally I’m not a great fan of it… I feel uncomfortable with the sexist patriarchal history of marriage — originally it had nothing to do with love, it was about property and male social power over women. Just look at the language. An alternative meaning for the word ‘husband’ is to manage and control, which symbolises the way men have traditionally treated their wives.”

The campaigner added: “It’s a curious contradiction. There I am fighting for the rights of gay people to be able to love and have relationships that are recognised and validated by the state, yet I am not in such a relationship myself. It might be viewed as odd, yes. For many people, having a long-term partner and children is an essential element of their personal fulfilment, and I respect and support that. But it’s just not for me.”

On Wednesday, Peter Tatchell warned that the Marriage (Same Sex Marriage) Bill may still face strong opposition in the House of Lords – despite passing its second reading in the House of Commons.