Media: Keeping up with the all-night viewer: What kind of audience is at large in the small hours? Owen Slot looks at Channel 4's late-night line-up

Children of the Seventies may have enjoyed the return of The Clangers to the television schedules last weekend. If they were awake at 3.55 on Saturday morning, that is. Unlike Florence and Dougal, stars of The Magic Roundabout who made their comeback earlier this year, The Clangers were not primed for a new generation of children just home from primary school, but for overgrown children back from a late night out.

Channel 4 started to run through the night last Friday and will continue to do so on Fridays and Saturdays until Christmas. Dropping The Clangers into 'Late Licence', the name of the all- night schedule, adds further nostalgia to a package that includes repeats of Ready Steady Go, the Sixties pop show, the first TV appearance of the Sex Pistols and a whole night dedicated to the Velvet Underground. Along with repeats of modern pop programmes - The Word, Eurotrash, Naked City - it is a recipe for youth market consumption. Or, in the words of Nicey and Smashie, the Harry Enfield and Paul Whitehouse creations who presented last weekend's viewing: 'It is a great idea from the boffins at Channel 4 of putting the older sort of shows which nobody watched the first time round on all through the night when even less people are going to watch them.'

Bill Hilary, the boffin at Channel 4 in charge of 'Late Licence', is convinced that there is an audience of insomniacs for this cultish schedule, but he has a get-out clause: if it doesn't work, forget it. The next four weeks are a trial run: 'If there is an audience out there, then we'll develop it.' Success won't be judged solely by audience figures - Hilary says he hasn't even been given a target - though ratings of below 200,000 will probably mean that, after Christmas, late-night watchers will be restricted to ITV.

Is ITV worried by the competition? 'Not really, not with the scheduling that I've seen thus far,' Warren Breach, head of night-time television at London Weekend Television, says. 'There's a lot of recycled material. If I was making the effort to stay up until 3am, I would be a bit pissed off if a programme came up that was a repeat.'

And there's the rub for night schedulers. The audience is going to be small, therefore the schedule is never going to be heavily financed, so Channel 4 doesn't have much choice but to screen repeats. Hilary, however, doesn't see this as a problem. 'The minute you start to make it glossy then it becomes very LE (light entertainment) and I think you've got a problem.'

Hilary's schedule suggests that it is more important that the target audience finds the content 'cool' rather than notices whether it is original or not. Any viewers unsure whether Hilary has them in his sights need only see if they identify with the celebrity duos lined up to present 'Late Licence': Jack Dee and Mark Lamarr, Julian Clary and Jo Brand, Eddie Izzard and Rhona Cameron, and Paula Yates and Jools Holland.

''It's more to do with station identity than competition,' Hilary says. The sort of presenters selected for 'Late Licence' would probably alienate some watchers of ITV's late schedules, which have a broader range of programmes - what Hilary describes as 'the scattergun approach'.

The largest step forward in night-time programming was LWT's youth- oriented 'Night Network' in 1987. It only ran for a year, not because it wasn't successful but because the ratings wouldn't persuade advertisers to pay the premiums that were being demanded to cover LWT's costs. The night-time audience, however, is an unusual beast - not your standard family with two children, but as often as not a group of people swigging tinnies in front of the same screen - and since audience watchdogs could not record this, 'Night Network' may have been sent to an untimely grave.

More sophisticated technology, which can now measure the size of audience that videos programmes, has shown that the wrong people may have been watching the programmes all along. American Gladiators and WCW Wrestling, it turns out, were favourites of four- to 15-year-olds who would watch the recorded programmes the following day.

The question for schedulers is whether they can find a million people who stay up late. Eighteen days ago, ITV's networked screening of the world heavyweight title fight between Riddick Bowe and Evander Holyfield produced something of a coup by recording 1.1 million at 4.15am. But that's not the sort of programme or audience that Channel 4 is even considering.