Mathew Horne is exasperated. He’s done Chekhov, farce, a documentary about Boy George... yet when the actor is spotted in the street, the response is always the same: “Gav-lar!” No matter that it’s three years since he appeared as the eponymous Gavin to Joanna Page’s Stacey in BBC Three’s hit sitcom.

“People actually think I am him,” he sighs.

He’s not complaining really; the show was and continues to be good to him. But the 35-year-old does worry what these people will make of his latest role in Jamie Lloyd’s The Pride, in which he plays three characters, including a male prostitute.

Contrasting attitudes to homosexuality in the 1950s with those of the present day, certain scenes in the play are “a little more challenging” than Gavin & Stacey’s cosy Essex suburbia.

The timing of the play has proved pertinent on several counts – the Equal Marriage Bill came in when it was still in rehearsals, while later came reports of Russia’s clampdown on gay rights. The cast have since taken to holding up placards reading “To Russia with love” during curtain calls.

“It felt important,” says Horne, of their nightly protest.

“Although it’s just a little West End play, we’re still making something thousands of people are going to see. We wanted to make the right statement.”

Contrary to certain belief, Horne isn’t gay, although it doesn’t bother him when people assume he is. He rather enjoys the ambiguity. “I kind of think of myself as a straight gay man,” he laughs. “I definitely share a lot of stereotypically gay traits, just not the main one. I don’t want to have sex with men.”

A self-professed liberal, he was “devastated” when, in 2010, he and his comedy partner James Corden found themselves accused of creating homophobic characters in their ill-fated 2010 sketch show. “It was deeply upsetting and completely unfounded,” he says. “But it was at a time when all sorts of things were being thrown at me and James.”

He’s perhaps understating the case when he describes the period that followed the end of Gavin & Stacey as “a bit hairy”. After a lacklustre-to outraged response to the 2009 sitcom, the pair then made spoof horror film Lesbian Vampire Killers, which critics deemed an outright disaster. Then, to cap off an already terrible year, Horne collapsed from exhaustion when appearing in a production of Entertaining Mr Sloane and had to be taken to hospital.

He lay low for some time after that but now is able to write the period off as a good lesson in avoiding overexposure and pigeonholing. He hasn’t worked with Corden since, although they remain good friends and may still work together in future. “I think it was important to redefine ourselves as individual actors and not be seen so much as a duo.”

Hence Horne has appeared in a diverse collection of roles on and off screen, while his pal gets down to making Hollywood musicals with Johnny Depp and Meryl Streep. One might imagine there’s a little competitiveness between them but Horne insists that isn’t his style. “I only feel positive and supportive when my friends do well. I kind of think that as long as I can feed myself and keep doing work I’m interested in, that’s all that matters.” So he doesn’t secretly yearn for a blockbuster role? “I’ve never been ambitious,”

he insists. “And I’m glad about that because it can be quite an ugly trait. I just wanted to make people laugh occasionally and be able to buy a house.”

Brought up in Nottingham, Horne developed a taste for performance at the age of nine and went on to study drama at Manchester University – the first time, he says, he had ever met anyone “posh”.

He has always dabbled in music, appearing in music videos for bands including The Maccabees and presenting the 2008 NME Shockwaves tour.

“But I never wanted to be more than a fan. I can’t play anything for a start.

I just love going to gigs. I’m a grownup groupie really.” It’s telling that he concedes if he were to be in any sort of band it would be “something like Orbital, where I don’t have to talk to the audience much and can just play nerdy music”.

While at university, he went to the Edinburgh Fringe as part of a sketch duo but comedy was only ever a means to get into acting, he says. It worked.

While up there he was spotted by comedian Catherine Tate who cast him in The Catherine Tate Show.

“It changed my life to have someone who was going places in her own right pluck me from the stand-up circuit.” The pair are back together again ten years later for Nan, a BBC One spinoff show based on Tate’s sweary grandma character that aired last Saturday. Horne plays her grandson and couldn’t be more pleased. “She’s a constant inspiration and a great friend.

I think she’s the funniest woman in the world.”

Horne loves strong women, and cites his mum’s “strength, intelligence and humour” as the standard by which all potential girlfriends are measured.

A “serial monogamist”, he’s currently single after the end of his last long-term relationship and “waiting for the next one”. Previous plans for children will have to wait, he says. “I’m too busy for all that at the moment. It’s hard enough deciding what to wear to the theatre let alone think about bringing a new life into the world, but maybe in the next four or five years.”

When The Pride finishes, his focus will switch to Nan and a new series of Bad Education, the school sitcom written by Jack Whitehall, in which Horne plays hypochondriac RE teacher Ben Birkett.

He’s reluctant to make any predictions for the return of Gavin & Stacey. Larry Lamb – who plays Horne’s on-screen father – claims there’s “not a chance in hell” of a new series. Still, they remain a close-knit cast.

“Larry’s like having a second dad,”

says Horne. “He has such a zest for life.

He came to the press night of The Pride.

Alison [Steadman, Horne’s on-screen mum] came to see it too and sent me a card that said, ‘I’m in tonight my little prince’. They’re great.”

l Mathew Horne appears in The Pride at Theatre Royal Brighton from Tuesday, January 14, to Saturday, January 18.

For tickets, call 0844 8717627.