The story now is so well known it's become almost a cliché: boy meets girl; boy hits girl over the head with a large stick; boy's sausages get eaten by a crocodile. Yet still the audiences lap it up. It's an overcast Sunday afternoon, and Punch & Judy is playing to a packed house on the Brighton seafront.

Joey the Clown, the warm-up puppet, enters stage left. "This is a joining-in show," he announces to the huddled mass of four and five year olds, "so everyone please join in. Will you do that for me?" (Muted response) "WILL YOU DO THAT FOR ME?" (Loud "Yes!", prompted by parents, standing towards the back).

Over the next 15 minutes, the familiar tale unfolds. "That's the way to do it!" says Mr Punch, whacking Judy for expressing feminist sentiments. "That's not the way to do it, is it boys and girls?" she protests. Audience opinion seems divided. The "Oh yes it is!" faction is perhaps slightly more vocal. There's near universal agreement, however, that the policeman - a rather severe character dressed in a Victorian-style uniform - has it coming.

As the blows are exchanged and the players have their exits and their entrances, it's interesting to observe the adults. They're not so much watching the show, as watching their children watch the show. And that, as every Punch & Judy man will tell you, is the way to do it. If Mum and Dad see that their offspring are enjoying themselves - and on this occasion they certainly seem to be - they're more inclined to cough up at the end when the man comes round, rattling his collection box.

At the end, having outwitted both the forces of law and order and the Devil himself, Punch takes his curtain call. With this, I contribute £1 and then make my way backstage to meet the stars. How did it go? Mike Stone, or "Sergeant Stone", as he bills himself, is slumped in the booth, still catching his breath. Like the late Donald Wolfit, he always feels totally spent at the end of a successful performance. "It was electric!" he finally gasps, spitting out his swazzle.

Stone, a somewhat weather-beaten 45 year old, has been Brighton's resident Punch & Judy man since 1974. Unlike most, he has a traditional theatrical background, having started in weekly rep: "I worked my ticket, shifting scenery and making tea, and occasionally getting the chance to walk through the French windows and say `Anyone for tennis?' I eventually progressed to the bigger rôles, like Hamlet and Richard III. But I soon discovered I wasn't much good at ensemble playing. I was too unpredictable, which used to confuse the Hell out of the other actors."

Nevertheless, he persisted, encouraged by an enthusiastic agent who held out the prospect of imminent stardom. It was in Tesco in 1974 that his Road to Damascus experience eventually occurred. "I'd been dressed as a Jaffacake for two days, giving out free samples. Suddenly, the thought struck me: `Do I want to do this for the rest of my life? No - the traditional theatre is obviously not my true métier.' I quit there and then."

Soon after, Stone discovered that Brighton council was looking to hire a new Punch & Judy man. The previous incumbent had died some 15 years before but, up until then, no-one had noticed. Stone, now unemployed and hungry, decided he had nothing to lose, and so applied.

"I told them a little white lie: I said I actually was a Punch & Judy man. They fell for it and gave me the job. Of course I knew absolutely nothing about the show, so I went straight to the public library and borrowed an ancient tome called `How to Perform Punch & Judy'. I read it and, with the help of a few friends, built the booth and all the puppets. It cost me about £150 to get it together. Then I set up on the beach, near the kids' paddling pool, and starting shouting at my hands. I've never looked back."

Hasn't it been a bit like playing Macbeth for 22 years, non-stop, albeit with a swazzle? "People ask me if I get bored performing the same script, year after year. But I don't perform the same script. Yes, it's essentially the same story, but the words come out differently, depending on the reaction of the children. Because every audience is new, so is every performance. I always work hard to make it as fresh as it was the first time I performed it. This goes for all good Punch & Judy men, which is why the show has endured."

There's some dispute over its origins. Most experts believe that Punch & Judy is a fusion of a medieval English mummers' play - St George and the dragon - and the clown troupe acts of the Italian commedia dell'arte, who toured Europe between the 16th and 18th centuries. These featured such characters as Harlequin, Colombine, and Punch's ancestor, Pulcinella (which means "little chicken"), a mischievous hook-nosed hunchback.

There were two distinct traditions. The northern Italian was more highbrow, featuring poetry and singing. Pulcinella was just comic relief. The southern Italian shows, however, were much more into slapstick, with Pulcinella a central character. It was this version that Pietro Gimonde of Bologna adapted into a puppet show, using elaborate marionettes. In 1662, he performed it in England to rave reviews. Samuel Pepys records having watched "Polichinelly .. an Italian puppet play ..... which is very pretty, the best that I ever saw."

Over the next few decades, the characters became more anglicised, and Pulcinella acquired a wife, Joan (sometimes Joannie). But the show's transition into the form we know today was largely the work of another Italian, Giovanni Piccini, who arrived in England around 1785. By then, the lead's name had been corrupted into Punch, Pulcinella having proved too much of a mouthful for British audiences. Piccini further refined the story. He gave Punch a jester's cap, in place of the Regency flowerpot topper he'd previously worn, and renamed his wife Judy. And significantly, Piccini used glove puppets, as opposed to marionettes, and performed his shows, not in a conventional puppet theatre, but from a portable canvas booth.

"I like to think this was so he could pack up and escape more easily whenever the police chased him," explains Stone. "Punch & Judy was regarded by the authorities as highly subversive, the Spitting Image of its day. It was one of the more popular side-shows during public executions at Tyburn, for instance. The highlight was Punch tricking the hangman into hanging himself, which couldn't have gone down too well with the law and order lobby. The Church hated it, too, because in the finalé, Punch triumphed over the Devil and escaped Hellfire."

The show remained a bawdy, adult entertainment until the 1850s. Then, following a Royal Command Performance at Windsor Castle, Punch & Judy suddenly became respectable. Ladies and gentlemen of quality started inviting the performers into their homes. But to protect delicate sensibilities, they were asked to tone down their act. Accordingly, the Devil was replaced by a crocodile, the hangman was eliminated altogether, and Judy, who in the Piccini version was something of a shrew, became a very genteel Victorian lady who took her bashings with good grace. Thus it was turned into a fairly innocuous children's show, which remained largely unchanged until the early 1970s, when Stone and other revivalists put new life into it.

"I helped give Judy her heritage back. My Judy is the Lucille Ball of the puppet world - a very feisty lady who doesn't take any nonsense. I also re-introduced many of the traditional characters, like the Devil and the hangman. But I like to alternate them between shows, so that different performances feature different characters. Today, for example, the hangman has taken the afternoon off. "(Actually, he was away being repaired, his nose having fallen off the previous week.)

What with the hangman and Punch's excesses, isn't it a bit violent for children? "Sometimes I get criticised by the PC brigade who say that Punch & Judy encourages wife-battering. Of course that's patent nonsense, like saying Goldilocks and the Three Bears encourages squatting. Children don't put such a serious construction on violence as adults, who try to psychoanalyse everything. They see Punch & Judy simply as innocent, knockabout fun, like Tom and Jerry."

However, it clearly isn't as sophisticated as a cartoon or television entertainment. How does it manage to compete?

"I think the thing that keeps Mr Punch alive and the children enjoying themselves is that it is a live show. When else do children get to see a live performance of anything? When else do they get a chance to actually join in? I know it sounds like an old hippie cliché, but I'm not so much performing at the kids, as performing with them. We make the show between us. This is what appeals to them. And I want to make children realise that live performance is best. Sod videos, the Internet and interactive CD-ROMs. Unless people keep live entertainment going, it will disappear."

Twenty years ago, Punch & Judy almost did, as traditional seaside performers began to go the way of the traditional British seaside. There were attempts - mostly disastrous - to modernise the show. For example, a lesbian collective up in Yorkshire brought out a pacifist/feminist version. There was also a punk Punch in the mid 70s, complete with a mohican and safety pins. They didn't last. That the show has survived today is mainly thanks to a new breed of enthusiasts who, like Stone, have gone back to the old traditions. Unlike Stone, however, few of them are full-time professional performers.

"Most aren't proper Punch & Judy men at all," he says, dismissively. "They're people like bank managers who perform it at weekends as some sort of cathartic remedy for having refused their customers overdrafts over the previous week. Today in Britain, I reckon there are fewer than 10 full-time professional Punch & Judy men who, like me, work their own beach areas. I'm part of an endangered species."

Does he see himself staving off extinction? "Most certainly. I see myself performing when I'm 95. It will never earn me a fortune, of course. All I ask is a little coin in the box at the end of the show - a silver one, preferably. But what I do get is total and utter job satisfaction. When the audience and I build a really good show together, at the end, I'm as high as a kite. I've never taken drugs; I don't need them. Punch & Judy is the only drug I need."