The obvious place to start is the kiss. A man called Colin is saying goodbye to his boyfriend Barry. He gives him a peck on the forehead. Big deal. But this is 1987 remember. There are letters of protest, and calls to the BBC, and objections in parliament. Mary Whitehouse says: ban this filth! And the tabloids scream, in large, inky, outraged letters: this isn’t EastEnders, it’s EastBenders!

Thirty-three years later, I phone up the man who played Colin, Michael Cashman, and I say to him: you sometimes forget it was that bad, don’t you, now we have gay marriage and everything. But the reaction to soap’s first gay kiss really was horrendous. Some of it was violent – Cashman had a brick thrown through his window – and most of it was nasty, and a lot of it was scaremongering: an AIDS-plague hysteria that tried to marginalise LGBT people; one acronym used against another. “It was shocking and unrelenting,” says Cashman. “The language was vile, and some of the headlines we lived with, it was vicious. It was a pretty mean period.”

But then Cashman tells me about something else that happened to him. While he was in EastEnders, a woman wrote to him and told him she’d been watching the show with her two sons, who were seven and nine, and her nine-year-old said ‘why is Colin kissing Barry?’ and the woman said ‘well, as mummy loves daddy, Colin loves Barry’. “And that,” says Cashman, “was when I knew why the tabloids hated us because we were challenging everything they were throwing at us. We depicted an ordinary man, who happened to be gay, in an ordinary relationship.”

Cashman, who’s now 69, thinks it was this ordinariness, rather than the kiss, that was the real revolution on EastEnders. “Once people got over the shock,” he says, “Colin and Barry became part of that family of the Square. Take Dot’s terrible son Nick, who always gave her trouble. They chose Colin to kick Nick out of the pub, completely against stereotype. It was clever, it was courageous and it was artful.” Effectively, he says, a gay guy on the telly got on with his life and the lives of the people watching slowly started to change.

Inevitably, the show also changed Cashman’s life, although he remembers arriving for his first day on the show hoping it wouldn’t. He became involved in politics as an activist for Labour. He co-founded the LGBT campaign group Stonewall. And eventually, he became an MEP and Labour peer. Now, he’s written a memoir about it all and it’s a beautiful, vivid, and occasionally upsetting account of how much things have changed for Cashman, and for gay people, and for all of us.

The book starts by building a profile of a young boy who could easily be a character in EastEnders. Cashman was born in the Limehouse area of London, on a council estate on the edge of the Thames, and the family didn’t have a lot of cash. Things were also strained between Cashman’s mother and his father. If his parents were out for the night, he would sit up til they came home, poised to listen for the silence. A strained silence meant trouble was coming.

If the trouble was serious, Cashman’s mother would sometimes run out on the common balcony of their flats and his father would slam the door behind her and lock it. Cashman remembers that he’d wait til his dad was asleep and whisper to his mum through the letter box. Some nights he would get a chair and unbolt the door and let her in. Other nights, she would ask him to push her cleaning things through the fanlight so she could go to the work in the morning.

For Cashman, those sombre moments in the flat are still terribly vivid. “I can even see the chair with the spindles broken,” he says. “I can see me taking it from the scullery and placing it there and I think that did build my relationship with my mother – that’s why I was the deposit of her secrets and why I became sadly blind to my father. I couldn’t see there was a man there, that there was something wrong with the relationship. All I could see was that he was wrong.”

Cashman as a child was also keeping his own secrets. He has always lived in the East End and now has a house just 500 yards from where he was born and he tells me about a time when he and his late husband, Paul, were walking past Dundee Wharf, the old shipyard in Limehouse. Cashman pointed at the old gates of the yard and said to Paul “you know what, I think there’s a bit of me that’s still trapped in there.” He was referring to one of the darkest and most upsetting moments of his childhood.

It happened when he was running home one evening and a young man he didn’t know stopped to speak to him. The man asked him if he would like to earn a shilling and led him to the back of the wharf. Suddenly, the man put his hand over Michael’s mouth and pushed him into a trailer and pulled his shorts down. Michael struggled but the man raised his fist and snarled like a dog. Then he started making sounds like he was hurt, then it went quiet and the man told Michael he knew where he lived and ran away into the silence.

Coming to terms with that night has obviously been difficult for Cashman. He says he kept it a secret when he was young because he was worried what people would think of him; they would say that he’d asked for it and that he was really a “bummer”. Later, after he first started getting acting work, the man who was acting as his agent, known as Woodie, also sexually abused him and, again, Cashman kept it to himself. You survived, he says, you coped and you got out when you could.

Talking about it now, Cashman says he has tried to find the right balance of emotions over what happened. “As survivors,” he says, “we become victors if we’re lucky. We own what was done to us and we recognise it should never have begun. For a while, I did think I didn’t deserve anything better, but when that guy tried to rape me and I fought back, that was when I decided actually ‘no, I deserve to be treated better’ and I was lucky in my relationship with Paul. He brought me through it and he persevered and he made me understand it was okay, I could be loved and I didn’t have to surrender a part of myself and make myself hurt and vulnerable. That’s what he gave me, and so much more.”

Getting to that point was not straightforward, though, and some of Cashman’s book is about the relationships that didn’t work out, as well as some of the difficulties he experienced with Paul, sometimes because of his public profile as an actor and politician. But there is also great joy in the book - in the young Michael discovering the gay scene, for example, and sitting in all-night cafes listening to drag queens and prostitutes, or dancing in gay bars, in amongst the heaving male bodies, shouting above the music and being himself.

There’s a good chance that anyone who’s gay will also recognise Cashman’s early experiences of realising, and then coming to terms with, his sexuality. He tells me about his memory of a day his auntie Eileen was visiting the flat and she put a record on and Michael, who was about seven, danced and whopped along and his mum turned to Eileen and said “I think he’s one of them”. He panicked but knew they were right; the realisation that he was different was emerging at the same time as the realisation that he had to keep it a secret.

“I thought ‘they know what I know about myself’ and I didn’t think I showed it,” says Cashman. “And it’s that fear that, somehow, because people know you’re different, they will use it, and you become vulnerable. We found coping mechanisms. I think a lot of gay people are good at blending in. I remember one night, when I was young, in a pub, all locked in for a late-night illegal drink, somebody said to me ‘look at them, they’re freaks’ and I said ‘no, we’re not’ and he said, ‘no, I was talking about poofs’. And I said ‘I’m gay as well’. And he said, ‘you’re not on, because you could pass as one of us’.” No, said Michael, I’m not one of us, I’m one of them.

Cashman’s experiences at school were also difficult at times because of his secrets, and his sexuality, and his difference – he was starting to get work in the theatre after a talent scout spotted him in a school play and this inevitably singled him out. School in those days, in the 50s and 60s, he says, dared you to be different or get it wrong and it had a ready arsenal of weapons for when you did. He remembers his headmistress taking him to the front of the school and, in front of everyone, asking him ‘who do you think you are?’

“That hurt me,” says Cashman, “but I don’t think I realised I would carry it with me for the rest of my life. So often, when that little voice over my left shoulder says ‘they don’t mean you, they want the other Michael Cashman’, that doubting voice goes right the way back there to that moment in the school: who do you think you are?”

Cashman even heard the doubting voice in 2014 when he was made a peer after many years of activism with Labour and 15 years as an MEP. Interestingly, while Cashman thinks that, in many ways, life for gay people has hugely improved, he thinks that in politics generally it’s gone the other way and things have got worse. He means Brexit, obviously, but he also means the negativity towards politicians (which was one of the reasons he quit as an MEP) and the last few years of Tory government and the divisions in Labour between the Corbynites and the Blairites. Cashman finds it particularly galling the way many on the left distance themselves from Blair.

“I think we’ve forgotten how bad it was after 18 years of Conservative government,” he says. “The state of the hospitals, the schools, the injustice, and I’m always frustrated that we’re never good at recognising the positive that’s been done, we become obsessed with the negative. From 1997, Labour turned the country around – the minimum wage … the investment in schools … after Dunblane, banning handguns … ending hunting with dogs … bringing in an equal age of consent. I could go on and on. Of course, we should look back and say ‘we could’ve done that better’, but if you don’t give credit where credit’s due, we pile into the narrative that all politics is negative and all politicians are in it for themselves – that doesn’t help the country and it doesn’t help us develop a progressive manifesto.”

Cashman believes the negativity about politicians is part of the explanation for Brexit, but he also believes another part was negativity by politicians. “Brexit revealed a mean, narrow nationalism that I thought had disappeared,” he says, “The scapegoating of the stranger, the rise in anti-Semitism, of homophobia, xenophobia, but I think it’s happened over 40 years.

“I said to Blair when we were in government, ‘you have to say at the despatch box that we are bringing forward these measures based on our relationship with the EU and the work of our MEPs’. That way you introduce us into the national script of what is happened. Every government has taken credit for everything that’s positive and has blamed Europe for anything that is negative. It’s so easy to misrepresent it and that’s precisely what was done after 40 years of tabloid drip-drip – that’s what happened with Brexit. A decision based on absolutely the wrong information.”

Cashman’s hope is that, one day, we will re-join the EU, but it has to be said the publication of his memoirs finds him in a fairly downbeat mood about the state of British politics generally. While he celebrates the progress that has been made on LGBT rights, and it is undoubtedly partly due to his role in EastEnders, he is also wary about celebrating too soon.

“I don’t accept that homophobia has gone,” he says, citing the demonstrations outside schools in Birmingham over lessons on LGBT equality. “I went up there and the way I heard LGBT people described, I was shocked. So the homophobia is there and it’s wrongly allowed to coalesce within religious belief. It’s still there and it surfaces. Look at the US, look at the way they are attacking trans people here, which is why we can’t be complacent and we always have to defend what we have and at the same time remember that our rights don’t travel with us.”

Cashman is also personally fighting some of the battles he thinks still need to be won. He’s sad he had to felt he resign from the Labour party in May last year over Corbyn’s leadership, the party’s policy on Brexit, and anti-Semitism but he’s busy as an independent peer, most recently introducing a bill to provide posthumous pardons to armed forces personnel convicted of historic homosexual crimes. “We must never forget there are still people who are worried about coming out in case of what might happen to them,” says Cashman. We have relative equality, he says, but that’s not the same as equality.

But if we started the story of Michael Cashman’s life-so-far with the kiss, then we can end it with something else inspirational. Sadly, Cashman’s husband Paul died of cancer in 2014 and Cashman says he has to reconcile himself to that every day. But when he was sorting through some papers recently, he came across a letter he wrote to Paul in the early years of their relationship in the 80s. “I want to help you all I can,” he said to Paul in the letter, “and so the best I can do is to love you. I will love you and give you the security of a relationship as long as you (and I) need it.”

Forty years later, Cashman stands by those words. “I have to say, when I found that letter and read it, I was staggered because that’s exactly what we did – through the highs and the lows: we worked at it and worked at it because we both wanted it.” The letter may have been written a long time ago, but it feels like a bit of a manifesto for relationships, he says. It certainly worked for them. “To know that you’re loved is incredible,” he says, “and, as I said to Paul in the letter, not everyone has that.”

One of Them by Michael Cashman, Bloomsbury, £18.99