The PPE, the paranoia, the distancing and isolation… Writer Russell T Davies agrees there are “strange” parallels between the world of his new drama, It’s A Sin – about the Aids epidemic – and the Covid-19 pandemic we are currently living through.

Filming of the five-part series ended a month before the first lockdown in March last year, and now it’s about to air on Channel 4, and you’ll find you can’t stop thinking about the compelling characters long after you’ve watched it.

The plot centres around five young people who we first meet in London in 1981 (and who Davies says are all inspired by people he knew at the time) – gay men Ritchie (Olly Alexander), Roscoe (Omari Douglas), Colin (Callum Scott Howells) and Ash (Nathaniel Curtis), and their best friend Jill (Lydia West). As their lives collide and friendships blossom, there are romances, nights out and parties at their lively flat. But a new virus, HIV (human immunodeficiency virus) is on the rise.

It can lead to Aids (acquired immune deficiency syndrome), the name used to describe a number of potentially life-threatening infections and illnesses that can happen when your immune system has been severely damaged by HIV. As the decade continues, we see the group of friends tested in the most heartbreaking of ways.

“We all miss people who we’ve lost and, within the fiction, I wanted to create people you’d miss”, says Welshman Davies, 57, whose husband, Andrew Smith, died from a brain tumour in 2018. “I’d love viewers to be sitting there in 10, 20 years time going, ‘Ah, remember Ritchie? Remember that flat full of people? Remember that gang?’. If I can achieve that, I’m very, very happy.”

Alexander, 30, was excited to play a character whose attitude and response to the Aids crisis is likely to surprise the audience. “Ritchie’s is not necessarily a voice you would expect to hear in a TV show about this topic,” muses the Harrogate-born star, who is famous around the world as the frontman of the pop band Years and Years. “But Ritchie’s whole life is led by fear and a deep shame, and he’s hiding so much from himself, from his friends, from his family. And to cover all of that up, he’s decided to be the funniest, best-looking person in the room.

“He thinks if he can make people smile, get into bed with a boy; if he can get on stage, do a great performance; if he can shine in this way then he can overcome all the other stuff he’s hiding, and that I 100% related to. I just know what that feels like. I myself am a performer and I’m gay, and I’ve tried to think about my own shame and how that’s been internalised.”

It’s A Sin is a powerful piece of telly – funny, incredibly moving and, at times, painfully shocking. It explores how many people denied the existence of Aids when it was first being reported in the early Eighties (in one particular scene, Ritchie is seen listing conspiracies and rumours about it, such as, “It’s a money-making scheme for drug companies”). As the episodes continue, we witness the true horrors of the epidemic, and the prejudice gay men faced.

Alexander says the role has made him realise how many people are “unaware of this specific moment of history, and how people were treated”. It’s not just the younger generation, who weren’t alive when it happened, who have a lack of knowledge either. “There are people who were around at the time – and there are gay people who were around at the time – who have an awful lot to learn from [It’s A Sin],” suggests Davies, who’s famous for his five-year stint at the helm of Doctor Who, plus dramas like Queer As Folk and Years And Years.

“It’s very important to say that not everyone lived their gay life like this or concerned by this. There was one scene I was always dying to include – I never did include it – that happened for real, for me. I was once sitting in the pub with my mates and we were all getting ready to distribute leaflets and probably going on a march or something, and it was a gay pub, and a gay man came to us and said, ‘I’m sick of this. I don’t know anyone who’s got HIV and I don’t know anyone who ever will’. And that was that man’s point of view, he didn’t want to be defined by a virus and I think that’s absolutely fair. So, it’s a tricky one. Everyone could learn more, but I don’t want to be the person lecturing.”

Davies also says it’s important to note HIV is “a virus that’s still around”. According to the Terrence Higgins Trust, there were 105,200 people living with HIV in the UK in 2019. Around 6,600 of these are undiagnosed and so don’t know they are HIV-positive. There’s currently no cure, but with an early diagnosis and effective treatments, most people with HIV will not develop any Aids-related illnesses and will live a near-normal lifespan.

Discussing the reasons why people don’t get tested for HIV, Davies reflects on “awareness – it’s the shame and embarrassment over people talking about sex full stop”. In 2019, Queer Eye presenter Jonathan Van Ness spoke publicly about being HIV positive. Does Davies think it would help if more people were open about their HIV status? “Absolutely. And then the other end of the scale, you’ve got Gareth Thomas [Welsh rugby player who revealed he is HIV positive in 2019] being blackmailed over it very recently.”

“I have noticed a significant change, amongst friends of mine, literally over the past five years,” he adds. “I know three or four people who I have known for 20, 30 years who have just stepped up and said they’re HIV positive. No drama, just in passing – and you think, that’s enormously brilliant. There are signs of things getting better, definitely.”

It’s A Sin is set to be another huge hit for Davies. Asked where he’s going next with his career, he says he’s spending a lot of 2021 script-editing for other people, including actor and comedian Sir Lenny Henry. “It’s slightly ‘pressure off’,” he says. And as for Doctor Who? He says he doesn’t miss it, because he’s “still that faithful viewer”.

“It was the hardest work in the world. It’s a bit like saying, ‘Do you miss going down the gold mines?’ Most people, here in Swansea, think I still work on it,” he adds. “After the New Year’s Day episode, people literally said to me, ‘That was good! I enjoyed the daleks – well done’. They just think I’m the Doctor Who man.”

All episodes of It's A Sin are available on All4 now.