THE CRITICS: COMEDY: Sons of the son of Steptoe

Channel 4 Sitcom Festival Riverside Studios, London

Every year, Channel 4 sponsors a Sitcom Festival, and every year the cultural commentators wade in with their theories about why the genre is dead. The holy trinity of Dad's Army, Rising Damp and Fawlty Towers is cited as the last hurrah of the British comedy empire. And now, with Men Behaving Badly and Father Ted gone, we are condemned to a life without laughs.

That's nonsense, of course, although it's true that the sitcom has been overtaken by new forms, notably comedy-drama and parodies of chat shows, docusoaps and news programmes. And it's also true that most recent efforts have been about as funny as a dead dog. Typical was The Grimleys, a dismal stab at Seventies retro, which slid further and further into a comic coma until the ventilator was mercifully switched off.

So Channel 4 are doing their bit to revive the supposed corpse, albeit with precious little return so far. This is the fifth year of the Festival, and only Tunde Babalola's Exile and Tim Dynevor's Slap! have made it to the screen. Remember them?

At least Dylan Moran's Black Books, last year's highlight, is tipped to provide the first viable offspring. Can any of last week's three offerings emulate it? And did they provide any clues as to what makes a decent sitcom?

As Seinfeld, a comedy famously "about nothing", demonstrated, what's crucial in sitcom is the com, not the sit. The sit can be virtually anything. A quarter of a century ago, M*A*S*H engaged with the vicissitudes of war and managed to be funny. This year, the film Life is Beautiful tickled ribs with a tale of the Holocaust. As long as there are engaging characters and half-decent performances, it all comes down to the writing. If the jokes are good, it works.

The first two shows at the Riverside were perfect demonstrations that the set-up is merely the springboard from which a comedy can produce either a perfect pike with three-quarter turn or a terminal belly flop. Both were built on the Steptoe template; one was funny, the other wasn't.

Write Back Home, by erotic novelist Sue Welfare, is about an erotic novelist who goes back to look after his elderly dad, while God's Toilet, by Ben Cooper, a writer for EastEnders and Casualty, involves a homeless vacuum-cleaner salesman, taken in by an unemployed alcoholic who lives with his randy, apparently invalid mum.

Similar scenarios, but with a great yawning chasm of laughter between them. A typical line from Write Back Home: Dad (played by Windsor Davies, a neat reminder of the supposed Golden Age) is having a drink; son tastes it - "What's that?" he asks, "Tizer and paint-stripper?" A typical line from God's Toilet: Mum complains about her son - "He call me such names." "They're not names," the son says. "They're descriptions."

It helped that God's Toilet (which refers, according to a holy tramp who makes a slightly confusing appearance, to Chatham - "Yea, and all the Medway Towns") introduces unexpected elements. The mother is straight out of Joe Orton, spiking the lodger's coconut cake with Rohypnol so she can have her wicked way with him. And the opening scene is a superb set- up. The two lads are watching a porn film. The first line, after much grunting and groaning - on and off-screen - is: "So that's what your ex-wife looks like."

Write Back Home also has its quirky characters - a lascivious home-carer (brilliantly played by Brenda "Gayle Tuesday" Gilhooley) and a cursing, smoking Irish nun. But whereas God's Toilet fizzed and popped with good lines and climactic set-pieces, Welfare's play left one charitably disposed but with sides unsplit.

"There's nothing wrong with being a lesbian," says Mrs Suddenly, an eccentric villager in Road Rage, the third play. "I was a lesbian myself once, in the Fifties in Kenya." A few more lines like that and it might have worked.

Written by Chris Larner, musical director of comedy duo the Right Size (who feature in the Festival this week), Road Rage is about treehouse- dwelling road-protestors. Lots of genuine comic possibilities there, then, as well as limitless potential for cheap laughs at all those hippy types, and even a couple of characters who could be decently fleshed out if it was ever commissioned.

Which it won't be. There were plenty of capers, lots of slapstick and a couple of good jokes. Sadly, a couple just isn't enough.

C4 Sitcom Festival: Riverside Studios, W6 (0181 237 1075) Wednesday- Saturday