Edinburgh Festival / Final Day: Why the Right Size is huge: Hamish McColl looks a bit like Stan Laurel; Sean Foley doesn't. Miles Kington accepted an invitation to Stop Calling Me Vernon

About two weeks ago, when I was lounging around the Pleasance courtyard with some fellow midnight drinkers, there came a call for help. There was a show starting at a quarter past midnight. It was called Stop Calling me Vernon, put on by a group called the 'Right Size'. There were some critics turning up to see it, and it would be lovely if there were a bit of an audience as well . . . So bedtime was postponed and we trooped off to see the show, and I don't know what the reviewers thought, but that was how I came to see the best thing I have seen at the Festival this year.

There are two actors in the 'Right Size', both men, and they have devised a play which is often more like a silent-film comedy than a play, and sometimes more like a music-hall turn. In fact the skeletal story is about a music-hall duo, played by Hamish McColl and Sean Foley, who keep wanting to do more, but keep relapsing into their favourite gags, until one day through the post comes a mystery package which turns out to be a prompter's box, and once they have installed this prompter's box in their room, they find themselves doing a serious drama . . . Enough. Everyone I have met who has seen it has loved it, and not one of them has been able to describe it, and I can't either. Nor indeed can McColl and Foley.

They can say it is theatre rather than comedy, and devised rather than written, and based somewhat on their own working relationship, but as soon as you start writing in your notebook, the explanations dive sideways. 'A lot of what we do comes about by accident,' says McColl. 'When we were working on Flight to Finland, we hadn't even decided where it was going to be set, even though a lot of the action had been mapped out. Then one day we came across a scaffolding tower which was exactly like the side of a ship, and we decided then and there to set the action on a ship.'

'They loved it in Oman,' says Foley. 'Mark you, it's odd playing to the female part of the audience in Oman, as they are all veiled, and the only way you can tell that they are laughing is by the way they rock forwards and backwards.' They had trouble there with a scene where they scatter bread on the floor and tread on it. 'Great murmurings arose,' says Foley. 'We hadn't realised bread has sacred implications in Islam, and what we were doing was blasphemous. We were asked to substitute apples or something else.'

A conversation with these two takes shape rather as their plays must do - gradually, bumpily, and fascinatingly. But one thing that shines through is their love of that tradition of British comedy which has been temporarily submerged in stand-up comedy. Their heroes are very unfashionable ones: Eric Morecambe, Tommy Cooper, Michael Bentine, and the much earlier music-hall stars, notably Robb Wilton. 'We've made friends with a veteran performer called Johnny Hutch,' says McColl, the one who on stage reminds me a bit of Stan Laurel. 'Now he's into his nineties and he used to be in a group called the 'Seven Flying Hindustanis' or something, and he knows all those ancient routines. We wanted him to show us a few things, but first of all we thought he should see us at work. So we asked him along to see a piece called The Bath.

'We had invented a really good sight gag. There was a line like a washing line right across the stage with a thing like a shower curtain on it, and by pulling the curtain to and fro you could get people on stage, and props, and sometimes two people, without the audience knowing they had come on.' 'And similarly, get them off again,' says Foley, who doesn't look at all like Oliver Hardy. 'And afterwards Johnny Hutch said to us, 'Nice use of the wiper, lads.' We didn't know what he was talking about till it turned out that this sliding curtain thing we thought we had invented had been going strong in the music-hall for the last century.'

But they have kept inventing things, and a lot of them are on display in Stop Calling Me Vernon, such as a wonderful sight gag with a door, and others with tea cups, and transparent side wings, and of course the prompter's box. From time to time one or other of the two men bends down to talk to the prompter and you know there is nobody in the box, but each time a hand comes out of the box and grasps the actor, and you know it is only the actor's hand going into the box and coming out, but you quickly come to believe that there really is a prompter in the box, and when he has an effect on the action you believe it utterly.

'12.15 at night is a crazy time to be putting on a piece of careful theatre,' says McColl. 'But it was the only slot we could get. We were meant to be going to the Assembly Rooms, but they kept us hanging around for months before finally saying there was no room for us, so this late-night slot at the Pleasance was better than nothing.'

They are not grumbling, though. Despite an almost total absence of reviews, except for a nice one in this paper, the legendary word of mouth at Edinburgh seems to have done the trick, and they are getting houses of 140 or 150 every night. And this week they are switching to 4pm instead, as a gap opens up. What are they going to do with their new-found free evenings? 'Sleep,' says McColl. 'It'll be nice to sleep when it's dark. We've done most of our sleeping by day.'

Sean Foley and Hamish McColl are two exotically Celtic names, but it's all in their forefathers; they look and sound as English as you like. In fact, Hamish even calls Sean 'John' or 'Johnny'. Hamish calls himself the straight man in the partnership - 'I tend to be the one who says, 'Stop messing about', while Johnny does the physical slapstick,' - but from where I stand both are extremely funny. A lot of the comedy is subtle and if you blink you can easily miss a gag or two, which means that they suffer from being called intellectual. But, says Foley, 'They aren't intellectual jokes, they're just intelligent.'

People all over the world have seen and laughed at the 'Right Size', from Oman to Ghana to Brazil, though this particular production has only previously been seen immediately prior to Edinburgh in Colchester and Barnet. How would it go down in, say, Ghana? 'They love us in Africa,' says Foley. 'This is for two reasons. One, they think our stuff is funny. The other is that it tickles them to see two white men being daft.' I agree with the Ghanaians. The 'Right Size' was the funniest and cleverest thing I saw at Edinburgh in 1994 and I hope they cut that out and use it next year.

'Stop Calling Me Vernon', Pleasance (venue 33), 60 The Pleasance (031-556 6550). 4pm. To 3 Sept.

(Photograph omitted)