Peter Tatchell recounts in this interview how he prompted  David Cameron and Boris Johnson to declare their support for same-sex marriage. He also defends the right of anti-abortion campaigners to engage in peaceful protest outside abortion clinics, including the display of pictures of foetuses.

But on arrival at the 66-year-old activist’s council flat in south London, it was impossible not to start by exclaiming at the sight of his sitting-room, so crammed with piles of paper there is only enough floor space left for a small desk, two chairs and, against one wall, three bicycles.

The papers, many yellow with age, support a white layer of campaign materials in current use. The sheaf of posters next to the visitor’s chair read: “Chechen tyranny and Islamism crushes all human rights.”

Tatchell’s work as an LGBT human rights campaigner extends to many different countries: “We’re doing a campaign round LGBT persecution in Chechnya, and against the way in which 36 out of the 53 Commonwealth states still criminalise same-sex relations.”

But a vein of humour runs through his talk, and he loves to spring surprises, as on the occasions in London and Brussels when he attempted to carry out citizens’ arrests on Robert Mugabe. This interview was punctuated by laughter.

The walls of the sitting-room are decorated in collages done a long time ago by Tatchell himself, and against one wall the back of a sofa can be discerned, but no one has sat on it for the last 15 years, for it too is swamped in papers.

ConHome [wondering about a metal device sticking through the sea of paper]: “Is that an exercise machine?”

Tatchell: “A rowing machine.”

ConHome: “And when was that last used?”

Tatchell: “Probably two years ago. But I do a daily work-out of 60 or more press-ups, a hundred and twenty transverse sit-ups, and sixty squats.”

ConHome: “Crumbs.”

Tatchell [pointing to his stomach, clad in a green shirt]: “So for my party trick, punch.”

ConHome: “No.”

Tatchell: “Come on, punch.”

ConHome [accepting it would be rude not to punch, but determined to do so as lightly as possible]: “OK, but I don’t want you to suffer Houdini’s fate. OK, I’ve punched Peter Tatchell.”

Tatchell: “In the 40 years I’ve lived here – 40 years in November – we’ve only had two murders in the courtyard outside, and one man hacked to pieces with a machete on the stairwell.”

ConHome: “A third murder?”

Tatchell: “No, no, he survived. But it’s much less rough now than it used to be. I was the target of incredible harassment and violent campaigns by neighbours.” He added that there have been “50 violent attacks upon the flat – mostly bricks and bottles thrown through the window” but extending to “a bullet dropped through the letter box with a death threat”.

ConHome: “When were they at their height, these attacks?”

Tatchell: “Late Seventies through to early Nineties.”

ConHome: “You seem rather proud of these battle honours.”

Tatchell: “I could have done without them. Within two weeks of moving in here, two of my Jamaican neighbours turned up on the doorstep and said, ‘We heard you’re a queer.’ And I said, ‘So what?’ And they replied, ‘In Jamaica we stone them to death.’

“Which I took as an almost veiled threat. But within a few months I’d turned them. They came round and they were fine. The initial period was quite scary. But my other Jamaican neighbours were wonderful. They said, ‘We heard you’re gay. We don’t care. Live and let live.'”

ConHome: “The other day you had a letter in The Times, which you signed along with various other people. It would be fair to describe you as a man of the Left, who was a Labour parliamentary candidate in Bermondsey in the early Eighties and is now a member of the Greens…”

Tatchell: “Yes.”

ConHome: “…but unlike most socialists, or indeed Greens, you sign letters and join campaigns with organisations such as the Freedom Association and the Christian Institute – for example your recent letter defending the right of anti-abortion campaigners to protest, or the campaign a few years ago in which you opposed the introduction of Extremism Disruption Orders.’

Tatchell: “And got the insult clause removed from the Public Order Act of 1986. We felt that insult was too low a threshold to criminalise someone and lots of robust criticisms could be construed as insults – and they were. So for example a young guy was arrested for holding a placard saying Scientology was a dangerous cult.”

ConHome: “Really? That’s abominable.”

Tatchell: “An Oxford student was arrested for joking that a policeman’s horse was gay. So with the same coalition – David Davis, the Christian Institute, the National Secular Society – we pooled our resources and we successfully persuaded the Government to remove the insult clause.”

ConHome: “Have you done anything with David Davis since he came back into government?”

Tatchell: “No. He’s obviously constrained a bit. But I’m a great believer that people across the political divide sometimes need to sink their differences and work together for the common cause.”

ConHome: “What’s the difference between you and someone who buys the Left’s package deal, which would include utter horror at the idea of standing up for abortion protesters? What’s the difference between you and Corbyn? You’ve known Corbyn for a long time, but then you did that very enjoyable thing, you interrupted his speech when you thought he wasn’t saying the right things about Syria.”

Tatchell: “Well it was me and a group of Syrians protesting at Labour’s failure to push in Parliament for humanitarian aid drops to the besieged civilian population in Aleppo.”

ConHome: “What’s the difference between your mentality and the mentality of a Momentum member or indeed just someone on the Left who would never dream of letting their signature appear next to the Christian Institute or the Freedom Association?”

Tatchell: “I judge issues by the principles involved, not on who’s supporting them.”

ConHome: “And who are the Tories who over the years you’ve found receptive? You’ve mentioned David Davis. Who else?”

Tatchell: “Well of course during the battle for LGBT rights, I worked quite closely with Edwina Currie, and supported her bid to equalise the age of consent. And before that, people like Charles Irving and Robin Squire, who were great Tory champions of LGBT human rights.”

ConHome: “I saw you weren’t invited to the party at Number Ten to celebrate Cameron’s introduction of same-sex marriage.”

Tatchell: “I’ve never been invited to any of the Downing Street LGBT receptions ever.”

ConHome: “By anyone?”

Tatchell: “Not by Tony Blair, not by Gordon Brown, not by David Cameron.”

ConHome: “It seems completely ridiculous not to invite you.”

Tatchell: “I was told that David Cameron’s aides were terrified that I might try and kiss him, or superglue myself to the Cabinet table.”

ConHome: “Oh I see. But in fact you would have behaved yourself?”

Tatchell: “Yes. If I’m responding to an official invitation of course I’m on my best behaviour. It’s when I don’t get an invitation people have to worry.”

ConHome: “Have you met Cameron?”

Tatchell: “Yeah, yeah.”

ConHome: “How do you get on with him?”

Tatchell: “Fine. The last time I met him I bumped into him in the street, outside Downing Street. I was part of a delegation from animal rights organisations calling for an end to the use of wild animals in circuses. Stanley Johnson was part of the delegation. So together with Stanley I had a good natter to David.”

ConHome: “And have you spoken much to Theresa May?”

Tatchell: “The last time I spoke to Theresa May was just before the 2010 election. In the run-up to the 2010 general election the Conservatives were the only major party with no LGBT policies. So together with the activist Tamsin Omond I organised a flash-mob outside Conservative election headquarters at Millbank, under the theme of ‘David Cameron, where are your gay rights policies?’

“So in response to that protest, David Cameron arranged for me to meet George Osborne and Theresa May to discuss my concerns. So I met them and they listened. The big ask at that stage was for ending the ban on same-sex marriage, which both George and Theresa said they would think about.

“The parting shot from George was a very warm handshake and the words ‘Very nice to meet you again Peter’.

“To which I said, ‘I don’t think we’ve ever met.’

“To which George replied, ‘Yes, you came and spoke at my school.’ Which made me feel very ancient.

“To which I replied, ‘George, you obviously did not listen to a single word I said. You’ve turned out to be a Conservative.’

ConHome: “But actually you’re a member of the Establishment yourself, aren’t you.”

Tatchell: “I wouldn’t say that.”

ConHome: “No of course you wouldn’t. Virtually no member of the Establishment ever admits that they’re a member.”

Tatchell:  “The end result [of his meeting with Osborne and May] was very quickly afterwards, the Conservatives did produce a separate, mini-LGBT-plus manifesto.”

ConHome: “Of a reasonably satisfactory nature as far as you were concerned?”

Tatchell: “Reasonably. It said that they would review the ban on same-sex marriage.”

ConHome: “Were you surprised when they actually decided to scrap the ban?”

Tatchell: “Well in the end they concluded the review and decided to leave things as they were.”

ConHome: “Oh.”

Tatchell: “Until the Equal Love campaign, which I was part of, brought a legal case in the European Court of Human Rights, to end the twin bans on same-sex civil marriages and opposite-sex civil partnerships.

“We then contacted David Cameron’s office to say look, we’ve put this case to the European Court of Human Rights, we are fairly confident that the court will rule in our favour, wouldn’t it be much better, from your point of view, to look as though you’re not being forced to do this by Europe, which after all will only inflame the Eurosceptics in your own party, but also, why not take the credit yourself?

“This is a way you can detoxify the Tory brand. So I wrote him a little spiel, which it may be pure coincidence, but the wording he used at the Conservative Party Conference when he announced, you know, ‘I don’t support same-sex marriage despite being a Conservative, I support it because I’m a Conservative,’ that was taken straight out of my briefing. Which could have been entirely coincidental.”

ConHome: “But which had in fact been written by you.”

Tatchell: “Yes. Conservatives value commitment, loyalty, fidelity. They value marriage so therefore they should want more people to get married, and not exclude people. So I made the pitch that the case for same-sex marriage was profoundly a Conservative one. That the Conservatives should take ownership of it, because it chimed with their traditional family values.”

ConHome: “Yes, in those terms it worked for Cameron, especially as a great many older Conservatives were deeply distressed by it.”

Tatchell: “But before that, when Boris Johnson was first elected as Mayor of London, it was just the month before the annual LGBT Pride Parade. I calculated that it was very likely he would attend, so I thought this would be a great opportunity to publicly put him on the spot over whether he supported same-sex marriage.

“So sure enough Boris turned up at the front of the parade, all the media are there, I wiggle through their legs, jump up in front of him and say ‘Welcome, thank you so much Boris for joining us at LGBT Pride, we’re really glad you’re here, now tell us, are you going to be supporting an end to the ban on same-sex marriage?’

“And he did a typical Boris Johnson of fluffing [Tatchell makes a gargling sound], but then eventually he said ‘Yes’. And so it was all on the record, it was all recorded. And that was a real game-changer. Because being such a senior Conservative, giving his public endorsement for same-sex marriage, that really did change the terrain of debate.

“We then went and used his support to lobby individual Conservative MPs, with my full briefing about marriage being a Conservative value. So for example shortly afterwards I went to Norwich Pride, and Chloe Smith was on the panel, and so I asked her, ‘Chloe, will you be supporting same-sex marriage? Boris Johnson has.’

“Deep intake of breath, a slight attempt to evade the question, but then she came out in favour. Boris’s support made it acceptable and respectable for other Conservatives to follow.”

We had diverged from the subject of free speech, to which we now returned.

Tatchell: “I do not support the anti-abortion protesters, but I support their right to protest.  I’m a hundred per cent in favour of a woman’s right to choose, and oppose any intimidation or harassment against women going to abortion clinics.

“But if a protest is peaceful, and non-harassing, then it should be allowed, because that’s what a free and democratic society is supposed to be all about. We let people express their opinions and protest at things they object to. That has got to include the right of people I or you may disagree with.

“But I’ve had people come back to me since I signed that letter saying, ‘How dare you defend these evil anti-abortion protesters?How dare you fail to support the right of women to have a safe abortion?’

“Well of course I haven’t done any of those things.

“There is a de facto ban on anti-abortion protesters showing images of foetuses. People have been arrested and placards have been confiscated.

“Even though I find those images distasteful, they are factual, and people who hold the view that abortion is wrong should have the right to show a foetus, even though it may be graphic.

“All the evidence I’ve heard is that the Ealing anti-abortion protesters have mostly been silent, peaceful, dignified, and not at all harassing of the women going to the clinic. If there have been breaches, then there are plenty of existing laws to deal with that.”

ConHome: “Who are your political heroes, either living or dead?”

Tatchell: “Mohandas Gandhi, Sylvia Pankhurst and Martin Luther King.”