The real thing, or just another fine mess?

They may look like them and they may talk like them, but are any of this year's Edinburgh comedy duos true double acts, asks DJ Taylor

To glance over this summer's list of Edinburgh Fringe attractions – Rich Hall and Mike Wilmot, Bachman and Evans, Men in Coats – is to glimpse an elemental comic bedrock that, however superannuated or worn away, still offers a kind of fundamental source for the materials on which comedy is supposed to rest: the idea of the double act.

At a rough guess, the sight of two comedians, usually men, usually in an unequal relationship (officer and private, boss and employee) chipping doughtily away at each other has been a comic staple since the pre-Christian era. Graeco-Roman drama abounds in comic servants sachaying on stage to bicker with their masters, while most Shakespearian comedies contain queer little incidents that would not have been out of place on the stage of the variety hall three centuries later.

None of this undoubted continuity explains what we mean by the idea of a "double act", what it consists of, and whether – in its purest form – it can still be said to exist. Two comedians standing on a stage telling jokes don't count. Newman and Baddiel were never a double act: they were simply performers who found it convenient to work together. A better definition would be old, pre-Second World War label of "cross-talk comedians". This at any rate conveys something of the psychological currents on which the average double act took sail, a sense of the human interaction going on beneath the patter.

Traditionally, the double acts of the early 20th-century variety hall era consisted of a pompous straight man being continually interrupted by a half-wit. Usually there was some kind of physical differentiation – the straight man would be tall and thin, the stooge short and fat. Or Mr Serious would boom intermittently in a lugubrious fog-horn voice while the foil squeaked high-pitched inanities at his side. Whatever the discrepancy, the form was based on sharply opposed outlooks – cleverness undermined, high-mindedness mocked, pretension exposed.

The content, meanwhile, was born out of elemental short-circuits: words misheard, instructions misunderstood. "If I have a rabbit in a hutch and I buy another rabbit, how many rabbits would I have?" fall-guy Murray, of the celebrated Thirties bill-toppers Murray and Mooney, would demand of his superior sidekick. "Why, two of course." "No, ten." "You don't know your arithmetic." "You don't know my rabbits." It sounds deathly, but the audience reaction hung on the exchange of glances, the mounting exasperation, the thought that here, however well disguised, was a relationship.

However constricting the double act formula of the pre-TV era might look on paper, it offered a format which the genre's more inspired performers could subvert and redefine almost to the point of parody.

(Bud) Flanagan and (Chesney) Allen's stage act involved funny man Flanagan's embarking on a kind of free-association ("I saw the ships all coming into whiskey") punctiliously corrected by Allen ("You mean port").

Film and television, with their close-ups and reaction shots, played a significant role in the double act's development. To watch any Morecambe and Wise sketch for more than a few minutes is to become aware of a relationship that seems to exist at some distance beyond the medium. Like Flanagan and Allen, Eric and Ernie could be presumed to like each other, more or less, beneath the banter and the serial ripostes.

Some of the best double acts, on the other hand, were built on a foundation of mutual dislike. The sharpness of the exchanges between John Belushi and Chevy Chase on NBC's Saturday Night Live in the late 1970s derived from the fact that Belushi and Chase positively loathed each other. The battle fought out on screen was a stylised version of the wider personality clash.

As the Belushi/Chase stand-off demonstrates, double acts could also operate in formats well beyond the conventional framing of stage comedy. As TV transformed itself into comedy's principal medium, many of the most durable comic pairings flourished against the backdrop of the sitcom.

Dad's Army's Captain Mainwaring (Arthur Lowe) and Sergeant Wilson (John Le Mesurier) were essentially a double act who happened to function as part of a larger ensemble. There were the fundamental divides of status (Mainwaring the bank manager and officer, Wilson the clerk and NCO) and physical appearance (short, choleric fat man, tall, languid thin man), but above all a class twist that inverted the stock situation: the officer/bank manager turned out to be socially inferior to the person he was commanding. Over nine years, Lowe and Le Mesurier stayed locked in an eternal combat, each minor advantage lost within an episode. The same complex interchanges could be seen in Fletcher's banterings with the prison warder Mackay in Porridge.

All of this – low-level psychological warfare camouflaged by gags – is given a convincing historical focus by Ted Heller's latest novel, Funnymen. Fountain & Bliss, Heller's fictional double act, are American, born out of the fag-end of the pre-war vaudeville circuit, but all the essential components are in place: Vic, the tall, good-looking crooner habitually undermined by short, fat Ziggy; the act, which leaves the stage for radio and film, increasingly reflecting the tensions of their private lives; the humour ultimately won at immense personal cost. Perhaps in the end this is what gives the best double acts their almost spectral gloss: the thought of private agendas going on beneath the surface frivolities.

Plenty of comedy duos have wandered hesitantly across the screens and airwaves of the past couple of decades – from Little and Large down to the cheerless subterranea of Marc and Lard. Almost without exception, none of them could be classed as a double act in the proper sense. If the tradition survives it does so in some of the Paul Whitehouse/Harry Enfield sketches where there is sufficient depth allowed for the characters, and the character oppositions, to be built up. The "Smashy and "Nicey" disc-jockey spoof, for instance, was founded on the classic double act premise: dominant front man effortlessly imposing himself on weaker subordinate, but forever let down by vanity and ignorance, the joke peeling away to reveal only a gaping hole. As with Fountain & Bliss or half-a-dozen of their real-life forebears, the viewer came uneasily to rest before the classic outline of the double act: the two bickering comrades left alone with their inadequacies, and a kind of endlessly unsettling laughter in the dark.

'Funnymen' by Ted Heller is published by Abacus at £10.99