Film preview: Burke and Hare

It's a subtle distinction but one the fanboy actor wants to underline. After all, he is famously dweeby and particular when it comes to the minutiae of any myth, franchise or storied fictional creation, be it Star Trek, Narnia, Mission: Impossible or Tintin (all of which franchises he's working in).

The criminal pair, Irishmen from County Tyrone who had emigrated to 19th century Edinburgh, got into the cadaver business after a poor unfortunate died in their boarding house. "They sold his body to the Royal College Hospital and made a fiver," says Pegg, 40. "And they thought, shit, we could make a lot of money here…"

The ducking and diving duo did in fact try graverobbing. But a crackdown by the local authorities - in Burke And Hare, Ronnie Corbett plays a militia leader - meant the bottom had fallen out the market. And out of the corpses, because they were rotten.

"So they went into business supplying fresh bodies by actually offing people. And they made a lot of money. Seventeen bodies later they got caught."

A couple of other things Pegg, last seen on the big screen playing Scotty in 2009's hugely successful Star Trek reboot, would like to clarify. No, while filming Burke And Hare in Edinburgh earlier this year, he did not visit the strip bar of the same name.

And also, he points out, a disclaimer appears on screen at the top of the film: "Everything in this film is true. Apart from the bits that are not." This, he grins, "kinda sums it up. So it's an extrapolation from that idea. A lot of the ground facts are right but from that we've launched off into a black romantic comedy. It's not a horror film."

Andy Serkis, who has "played" Gollum and King Kong, as well as Moors Murderer Ian Brady and rocker Ian Dury, is Hare. His murderous motive is to help his wife (Jessica Hynes) live in the "finery" she expects. Pegg is Burke, in love with a part-time prostitute (Isla Fisher) and keen to help her fund her passion project, a play.

"So it's this very interesting thing that I think works very well in the film - you find yourself rooting for the bad guys the whole time. They are essentially evil - well, they're not evil, they do an immoral thing. But the film constantly encourages you to condone their actions. It also throws a great little argument out there, which is almost convincing: if they hadn't provided the medical sciences with so much research material at that time, medical science wouldn't have progressed in the way that it did. Because it was a real golden age for medical science, especially in Edinburgh. And thousands of lives would have been lost because of the lack of information.

"So," he adds, clearly pleased that his Burke errs more towards the "roguish" than the "serial killer" in the comedy, "you stay on their side right to the end. You feel sorry for them when they get caught."

The film has been some time in the making. David Tennant was originally due to play Hare, but when filming was pushed back, he had to pull out as he was filming the pilot for an ultimately ill-fated drama in the US. But Pegg kept the faith. He may be in serious demand in Hollywood (he shot Steven Spielberg's Tintin before Burke And Hare, and is currently filming Mission: Impossible 4 in Prague with Tom Cruise) but this is the kind of project he likes to be involved with: British-made mainstream comedy with an ensemble cast to die for. He was particularly pleased to be working again with Jessica Hynes, his old co-star in the cult Channel 4 sitcom Spaced.

"I'd forgot how much she makes me laugh. It made me think, oh shit, maybe we should have done a third series of Spaced - not that we could have because time didn't permit it. But…"

Burke And Hare is directed by John Landis, the veteran American behind, amongst myriad others, An American Werewolf In London and Michael Jackson's Thriller. Does this mean the murders are as gruesome as we might expect from a director with a winning way with lycanthropy and the walking dead?

No, insists Pegg. For one thing, Edinburgh's medical establishment required the bodies to be undamaged. So the Irishmen came up with "burking", the suffocation of their victims. "The gore in the movie comes entirely from the bodies on the slab being cut up by doctors."

Still, Landis is "old school" - he's not interested in CGI trickery added after the fact. He wanted "physical effects happening on the day, on set". Cue special "stunt" cadavers shipped over from specialist props makers in the US who also supply Quentin Tarantino with all his corpses. "We do have some great arterial blood squirts," says Pegg, almost licking his lips.

• Burke And Hare is in cinemas from Friday