Jonny Sweet: Playing the opposition

Amol Rajan meets David Cameron's alter ego, Jonny Sweet, who plays the Tory leader in a TV drama airing tonight

(Channel 4)

When, just over four years ago, Jonny Sweet turned up with a friend for his interview as satire editor of Varsity, the student newspaper I was then editing, it took him a matter of seconds to convey his suitability for the post. Literally by way of hello he ventilated the view that all student journalism is essentially tosh (true), and that student newspapers are therefore at their best when they don't take themselves too seriously (also true). This disposition made him and his accomplice, with whom he moved into a flat in north London last month, the best satire editors Varsity ever had.

With absolutely no budget, and very little time, they produced hilarious editions of the page, called News King. It specialised in the macabre, finding humour where there ought to have been none. One part contained captions below curious pictures, often found on Google Images. I remember seeing an image of a giant toe hovering perilously over a sharp pin, and wondering how on earth this could be made funny. Sweet and his co-conspirator managed it; the caption read: "Haemophiliac starts to tire of brother's "sick" joke". We laughed all night.

Fast-forward to now and Sweet has become one of the most successful comedians of his generation from Cambridge. Last month he was awarded the hallowed best newcomer award in Edinburgh for his show Mostly About Arthur. And tonight he hits national screens in a part that he may one day reflect on as his big break – in television at least.

"Until now I seem to have specialised in pilots that didn't get commissioned," says Sweet, "so you could say playing David Cameron makes a nice change." He plays one of two title roles in More 4's When Boris Met Dave, mischievously scheduled for the night before what is probably the Tory leader's last speech to a party conference as opposition leader.

The docu-drama recounts the tale of an infamous night in Oxford two decades ago, when Cameron and Boris Johnson, both members of the haughty Bullingdon Club, raucously toured Oxford, trashing all and sundry... except, one of them didn't.

"Cameron was actually very in control, and he never really got involved in the wilder shenanigans. He was in bed by the time it all kicked off," says Sweet. "Dave was very subdued and rather chilled out. He would watch game shows rather than mess with university politics."

When Sweet arrived for the audition with John Dower, the film's director, he wasn't told that it was for a role as David Cameron. The audition was conducted as a standard Oxbridge interview, in which Sweet was simply himself.

Last year he came desperately close to being cast alongside his close friends and co-writers, Jo Thomas and Simon Bird, in Channel 4's hugely successful The In-Betweeners, but missed out because he was "too posh". The irony isn't lost on him. "First I get rejected because I'm too posh; now I'm playing an Old Etonian. Figure that one out," he says.

Sweet, who hasn't met Cameron and says he wouldn't mind doing so, says the camaraderie on set – especially with Christian Brassington, who plays Boris – was fantastic. But not, he insists, because this was a hatchet job.

"I don't think the Tories will be all that angry after they've seen it," he says. "Cameron is rather opaque and difficult to impersonate, so if anything I had to rein myself in. There were times when I'd want to go big but was told to keep a lid on it."