It is 1988 in some underground, underlit London comedy club. A prematurely aged Irishman stands on stage, dressed in a shabby long brown mac, all bloodhound eyes and a droopy Wild West moustache, and utters another in a beautifully understated seam of immaculate one-liners. “A lot of people say to me, ‘Hey you’,” pauses, makes almost imperceptibly small gesture of dismissal “‘what are you doing in my garden?'” The audience takes a couple of seconds to catch up, and then dissolves into hysterics. The man is Michael Redmond.

The joke defines him perfectly as an odd, outsider character and hints at a host of other weird situations as yet unrealised. For once, the audience is made to use its own imagination. There are no clues, or helpful pointers. The line has little in common with most of the material of the other “alternative” stand-up comedians of the time; it doesn’t ask us to share an experience, as when three of the same bus come at once; it doesn’t contain any easy cultural signifiers, such as references to 1970s television or the forgotten play-ground rituals and newsagent confectionery of childhood; it isn’t “about” anything. The everyday phrase, “hey you”, is disrupted and made bizarre by being followed by the unexpected “what are you doing in my garden”. It is, to invoke a now wasted phrase, a moment of pure comic genius. Of course, appearing in print does no justice to it; it relies on the nuances of performance.

I first heard the “what are you doing in my garden” joke in 1987, when I was 19. My friend Terry, who had been to see a proper London comedy gig, did it in a student show and cheekily let everybody think it was his own. The next time I heard it was when I shared a bill with Michael Redmond himself, in 1989, trembling with nervous admiration. And I heard it for the last time just last month, when mainstream comic Joe Pasquale told it for the delight of the Queen and the Duke of Edinburgh at the Royal Variety Performance.

Pasquale’s act that evening was a triumph, the undoubted highlight of the show, and he worked the Dominion Theatre audience with a skill that made the huge venue seem intimate. Despite learning his trade on the mainstream circuit and working with scriptwriters rather than producing all his own material as most of the alternative comedians do, Pasquale feels he has more in common with the Goons than with the 1970s club acts such as Mike Read and Ben Elton’s bete noir, Bernard Manning. He’s looked past them to rediscover a delightful and engaging brand of Tommy Cooper-esque silliness that stretches way back to the last days of music-hall tradition. But Pasquale did use some material that seemed familiar, with lines and visual jokes similar to a number that have been performed by “alternative” acts such as Martin Soan (a balloon-modelling bit involving a catwalk-style wearing of an uninflated balloon), Boothby Graffoe, (“My girfriend said, ‘I can’t see you any more.’ I said, ‘I’m behind the settee.'”), Arthur Smith (the “I Know a Song That’ll Get on Your Nerves” song) and, of course, Michael Redmond.

Soan, who says Pasquale also does a routine with a tiny voodoo doll of himself that’s like one Soan made up in the 1980s, finds this upsetting. “Thinking about it gives me the shivers. No because I don’t think Pasquale’s any good, but because it’s just depressing when you see him up there. But he may have done it entirely innocently.”

Historically, so-called “alternative” comedians, with their post-punk aspirations towards some vain ideal of artistic integrity, have been as quick to demonise the old club-scene comics as amoral thieving magpies as the club-scene comics are to paint them as humourless middle-class lefties who wouldn’t know a decent joke if they saw one. But now hostilities are ceasing and both camps sit comfortably alongside each other on Gag Tag, Jack Dee’s Saturday Night, Fantasy Football and Have I Got News for You.

Traditionally, mainstream acts aren’t precious about material in the way that their alternative comedy cousins are. To them, jokes are just jokes, naturally occuring phenomena, like wind or rain, resistant to the abstract notion of ownership. When London circuit comedian Nick Wilty found himself doing warm-up for Granada TV’s special of the old mainstream show The Comedians, in 1993, one of the performers gave him a lift back to London. Entering the Blackwall Tunnel, the comedian said to Wilty: “You had some good lines there, I can’t wait to put them in my act.” “He wasn’t trying to hide anything,” remembers Wilty, “he just genuinely had no idea that I’d be pissed off. He didn’t appreciate that my material was written by me.” Backstage on The Comedians, the acts bicker about who is going to do which jokes and flip coins for the honour of performing any new gags that they’ve all heard.

The gag-writers who supply mainstream acts with their jokes obviously share this outlook. London clubs are regularly full of bit-writers and researchers scribbling down notes, and last November Stan Nelson, the floor manager of The Comedy Store, actually ejected a man who was surreptitiously taping the evening’s performances. Pasquale, of course, uses writers, but said that he wouldn’t wittingly use someone else’s act. “It’s impossible to know where to stop, though,” he adds, “you get so many people telling you jokes.” Ideally, routines as told by comedians, as opposed to jokes told by blokes in the pub and cab drivers, will reach a stage where they are impossible to plagiarise. In the year 2525, the futuristic supa-comedian in his silver suit will have developed an act so distinctive and steeped in his own individual specialised world view, that his lines would be incomprehensible in the mouth of anyone else, and we can see the beginning of this evolution in the work of Harry Hill, Simon Munnery and, er, Eddie Izzard. In the meantime, most jokes are still viewed as part of the public domain.

On the “alternative” circuit the obvious fallacy of the spontaneous generation of material, authorless and fully formed, out of thin air, is vilified, and any duplication of material is seen as theft, even when it could realistically be mere coincidence. This is especially true of topical humour, dealing as it does in a limited range of personality or news-based observations. Most satire has a crushing air of inevitability about it. A member of The Comedy Store’s “Cutting Edge” team a weekly news-events based show told me Spitting Image had stolen his idea of Frank Bruno doing pantomime routines in a boxing ring. But there are thousands of people making a living out of topical humour in Britain today, and Frank Bruno is only known for two things pantomimes and boxing. It wouldn’t take an infinite number of monkeys to think of these two elements and come up with the same result. In fact, it would take two monkeys, perhaps sharing one typewriter.

Musical comedian Jim Tavare says he can remember the exact moment of the birth of “what are you doing in my garden?” In the summer of 1987, he and Michael Redmond had been performing at the Screaming Beavers comedy club in Macclesfield and were staying at Tavare’s parents’ house in Prestbury. Looking out of the window while they were sitting in the lounge drinking tea, Jim, Michael and Jim’s brother saw a distressed man running around in Jim’s parents’ garden. According to Jim, they rang the local mental hospital, who sent someone around to pick up the escapee. Later that evening, Redmond wrote his legendary gag. Redmond himself, however, has no memory whatsoever of thispeculiar incident, which made such an impression on Tavare, but recalls the thought processes by which he arrived at the line. “I’d been worrying at the idea for ages. I thought of ‘Hey, you, what are you doing in my kitchen?’,” he says, “but that seemed like too much of an invasion of privacy, too threatening. I changed it to ‘garden’ and it worked.”

In contrast, Pasquale’s manager Michael Vine says that, as far as he is concerned, “a new gag is only a gag you haven’t heard before”. With regard to “what are you doing in my garden?”, he says he “associates the line with the public domain”, and that it seems to suit Pasquale’s bumbling innocent persona perfectly. It is true that when Pasquale and Redmond both tell the joke the image conjured up is quite different. On seeing Redmond in your garden you would think: “Wow! A tired Jesse James is in my garden. Why?” On seeing Pasquale, you would think: “Hey! There’s Joe Pasquale from Thames TV’s He’s Pasquale, I’m Walsh. And he’s in my garden! Whatever can he want?” As for Pasquale himself, he has an innocent explanation for how “what are you doing in my garden?” found its way into his act. In 1993, he was playing Silly Billy in Jack and the Beanstalk in pantomime. Phil Nice, the former double-act partner of playwright Arthur Smith, was the pantomime dame. On discovering Silly Billy planting beans alone on stage, Nice would shout: “Hey you! What are you doing in my garden?” The following year, Pasquale had the idea to use this line of dialogue as an actual gag in his Blackpool summer-season stand-up set. Coincidentally, the sound technician told him it was his favourite joke, and he had been entertaining his mates in the pub with it for years already, although even he didn’t know where it had come from. And, after a day on the phone, vainly chasing the flickering spark of the creative imagination, I, too, was none the wiser, and what has become perhaps one of the most compelling mysteries of the 20th century must remain unsolved.

For me, hearing “what are you doing in my garden?” for the first time opened up a vast world of potential comic possibility, of things that could be funny without really relating to anything, bypassing logic and satire, and crudity or stereotyping, and kitschy cultural references. Even Vine is moved to admit: “It’s just one of those lines, so simplistic. You think, ‘Why couldn’t I have thought of that?'” Indeed.

And so, to any young comedians reading this, a warning. If you are sitting at your window at night, trying to find a better word than “kitchen”, and you see a figure in the garden, do not allow them to look at what you are writing. Just tap the window and say: “Hey you…”.