A critic once asserted that all of Laurel and Hardy's work could be summed up in one phrase: "They hit each other and fall over a lot." You could quite easily apply the same description to Vic Reeves and Bob Mortimer, who lay into each other with the abandon that only the symbiotically linked can get away with. They are cartoon squabblers made flesh, the live-action answer to Tom and Jerry.

And even more popular. Reeves and Mortimer's books, videos and live tours have racked up sales that only double-acts of the stature of Marks and Spencer can match. Student union bars the length and breadth of the land echo to the sound of their catchphrases, "Uvavu" and "Eranu". Their spoof quiz-show, Shooting Stars, is one of BBC2's solid-gold ratings bankers, regularly notching up four million viewers. They claim the words "please, please" were used when the Corporation begged them to make the third series, which starts next Friday.

And to cap it all, they've just been granted the accolade, rarely bestowed on comedians, of an Omnibus profile on BBC1. "People are going to say, `Are we ready for an Omnibus yet?'," Mortimer concedes. "But we must be, because for a couple of years we've been turning down South Bank Shows and Heroes of Comedy. It's not for us to say, but the industry seems to think we're ready."

Resplendent in a mop of blond hair and a pair of Ipcress File-vintage Michael Caine glasses, Reeves (real name, Jim Moir) tries to put his finger on the double-act's success. "People like to be voyeuristic and look at others bickering," he surmises. "That's part of any double act, from Laurel and Hardy onwards. We're inseparable but irritated by each other's presence."

"Bickering is the be-all and end-all," chips in Mortimer, who looks less dandyish in a pair of spectacles held together with Sellotape. "Jim bullies me a lot of the time. Then, in a funny way, I get my own back, but Jim won't realise so he'll still think he's the king of the castle."

Paul Morley, who directs the Omnibus, comments that Reeves and Mortimer are "two very different minds that connect so beautifully. It's a match and a mis-match made in heaven."

For all the on-screen arguing, Reeves laughs that he and Mortimer are "Siamese twins. In its entirety, that's what we are. In an amoebic way." As they pick over sandwiches at the Groucho Club in central London, they certainly give the impression of being metaphorically joined at the hip. In the decade they have worked together since Mortimer got up out of the audience to take part in Reeves's act at the Albany Empire in Deptford, they have obviously worked their way under each other's skin. Their senses of humour have synthesised. They finish each other's sentences and top each other's punchlines. Their sheer enjoyment of one another's company is central to their popularity. Reeves and Mortimer see far more of each other than most married couples. Yet remarkably, they are still on joshing terms. "If we film two minutes, we've been together 48 hours doing it," Reeves explains. "We write together every day. We have to get on. You hear rumours of some double-acts who can't stand each other. That can't be true. You couldn't do it."

The longevity of their relationship means that much of their banter now comes intuitively. "You have to have a sixth sense," Mortimer says. "I know when Jim's got a bit more to say, so I try to keep my mouth shut. It would have to be scripted if you didn't have that. We come across as a proper double-act because we're filling in the little bits naturally."

In various guises - the cod variety show, Vic Reeves' Big Night Out for C4, BBC2's sketch show, The Smell of Reeves and Mortimer, and Shooting Stars - Reeves and Mortimer have now been on our screens since 1990, when Jonathan Ross famously twisted Michael Grade's arm to come to one of their live shows, and the C4 boss signed them up on the spot. There are still some people who are left cold by Reeves and Mortimer, though. Jim Davidson in the Omnibus film says he just "doesn't get it", and Reeves recalls a review in the Daily Telegraph which simply read: "Reeves and Mortimer - comedy?"

Reeves admits that they do have to keep a check on their more surreal meanderings by grading their lunacy levels. "We say, `that's Level 5, people won't understand that'. We now know that to be broadcast, a show has to be 30 per cent Level 1 and your Level 5 better not take up much over 10 per cent."

Despite all that, they are undeniably influential - new comics are often classed as "very Vic and Bob". Mortimer also contends that derivative material "has flooded the advertising world. The Tango and McDonalds ads wouldn't have been on without our sort of stuff."

There appears little likelihood of Reeves and Mortimer ever swimming in the mainstream, however. "We'll keep ahead of it," Mortimer promises. They remain gloriously unpredictable, following the aroma of originality rather than the stench of pre-set formulae. "If we tried to analyse our comedy, we might stop being any good at it," Reeves reckons. "If we started thinking, 'Why's this funny?', we might start incorporating rules into it. I'd be suspicious that it would change the nature of what we do."

They are already planning their next vehicle, a sitcom based on the Cox and Evans characters from The Smell of Reeves and Mortimer. It will no doubt have the same sense of inspired surrealism that has characterised all their work and led critics to dub them "the post-modern Morecambe and Wise". The joy of watching two people slug it out with giant frying pans is hard to beat.

Mortimer is quick to reassure anxious fans that the sitcom won't represent a huge departure for the duo. "We're not trying to reinvent our style," he soothes. "Our new programmes have always just been different vehicles for the same sort of comedy. A theme runs through it." Which is?, I ask tentatively. "Childish, slapstick silliness."

`Omnibus: The Film of Reeves and Mortimer' is on Sunday at 10.25pm on BBC1. A new series of `Shooting Stars' starts on 26 Sept at 9.30pm on BBC2