RICHARD and Judy have done it. So did Morecambe and Wise. And Desmond Lynam. But switching channels can be a risk for TV stars if they don't deliver ratings as big as their salary cheque.

When television stars want to change channels it's not as simple as pushing a button on the remote control to zap them from BBC to ITV or Channel 5 to Channel 4. There are clandestine meetings with agents, whispering in dark corners of the studio and midnight phone calls at home as the new contracts are negotiated. Switching channels not only guarantees a wage increase - and we're often talking lots of noughts - but maximum publicity, and with that comes the hitch. The bigger the star, the harder they fall down the ratings if things don't work out.

Richard And Judy - that's Richard Madeley and his real life missus Judy Finnigan, to the uninitiated - return to C4 screens next week with their daily teatime talk show. And, they claim, the move from ITV's This Morning was for artistic not financial reasons. This is often the case. A bigger pay cheque is all fine and dandy, but the chances are the performer wants to have more control over their career.

That was the case with Mr and Mrs Daytime Television. The arrival of a new daytime controller, Maureen Duffy, signalled the end of their stay on commercial TV. She was brought in to maximise ratings by taking it downmarket, according to Richard and Judy in their recently-published autobiography.

Finnegan found the internal politics difficult to cope with. "In the end, although we tried our hardest to go along with the planned changes, Richard and I, unable to feel wholehearted about some of these, decided to leave," she recalls.

Their success meant they were valuable commodities who could afford to sit tight and wait for the right conditions, but Finnegan was adamant that they wouldn't use the threat of leaving ITV to up their salaries at This Morning.

A producer friend asked if they'd like her to put out some feelers, without mentioning names. By chance, an ex-This Morning researcher who'd become C4's head of daytime factual programmes, happened to mention to this friend that her "Holy Grail dream" was to have Richard and Judy doing a teatime talk show for her network. The pair, with the producer, put together a treatment for a show. Money was worked out and eventually they were revealed as the new teatime faces of C4.

Everyone concerned knew the dangers of trying something new. The ratings for the new show have, reports suggest, not been as good as C4 had hoped. That's probably more a case of sour grapes than anything else as ITV attempts to regain the daytime audience.

Rarely does this channel-hopping goes smoothly. Ask Johnny Vaughan, who quit C4's The Big Breakfast for a lucrative BBC contract only to have the critics describe his debut comedy series 'Orrible as just that - 'orrible. Viewers felt much the same, as poor ratings demonstrated.

Bruce Forsyth was at the peak of his Generation Game fame when he left the BBC for ITV and Bruce Forsyth's Big Night, a compendium of programmes stretched across Saturday night. Reaction was poor, with Forsyth only finding success again by returning to game shows like Play Your Cards Right and You Bet!. He even went back briefly to the BBC before decamping to the other side again to present a revamped Play Your Cards Right and The Price Is Right.

Morecambe and Wise were Britain's most successful comedy double act. At least, that's how we remember them, but their relationship with TV yo-yoed between the BBC and ITV. Their first success was in The Morecambe And Wise Show on the commercial network. In 1968 they were tempted to move to the BBC, just as another TV funny man Benny Hill moved in the opposite direction.

Their scriptwriters, Sid Green and Dick Hills, were left behind as they were under exclusive contract to ATV. Happily, Eric and Ernie found Eddie Braben to write for them at the Beeb, where their Christmas shows became as much a part of the festive season as turkey and mince pies, attracting audiences of more than 20 million.

Eventually, Thames Television won Morecambe and Wise back in 1978, although their shows never achieved the ratings success of their decade at the BBC.

ITV bosses thought they'd won the television equivalent of the World Cup when they enticed presenter Desmond Lynam away from the BBC to front their Premiership series. The fact that he'd publicly complained about the late slot given to Match Of The Day by the BBC alerted them that he might consider a transfer. A sick-as-a-parrot feeling ensued when low ratings failed to justify the peak Saturday night slot with Des demoted to a late night alternative.

The signs are that top actors are no longer willing to be tied exclusively to one channel. Several, including Robson Green and Sarah Lancashire, have unlocked themselves from golden handcuff deals confining them to ITV.

Deals like theirs are sought by fleeing soap stars. Ross Kemp signed for ITV once he'd finished with Grant Mitchell in EastEnders. So did Martin Kemp after Steve Owen was killed off in the Albert Square soap. Both have new ITV series starting soon - Ultimate Force for Ross K and Daddy's Girl for Martin K.

Other ex-soap stars prefer to be free agents. Another Walford escapee, Tamzin (Melanie) Outhwaite, has filmed a BBC1 drama Red Cap and also has a role lined up in an ITV thriller.

Presenters too like to nip between channels these days. C5 announced recently that Carol Smillie, of BBC1's Changing Rooms and Holiday shows, would be making programmes for them. So will Clive Anderson, who moved to the BBC from C4's Whose Line Is It Anyway.

When Lily Savage signed up with ITV, she took the BBC's quiz show Blankety Blank with her. Frank Skinner and David Baddiel moved with Fantasy Football in the same direction.

Sometimes entire series make the switch. Men Behaving Badly was dumped by ITV after one series, taken up by the BBC, Neil Morrissey took over from Harry Enfield and one of Auntie's biggest hits was born.

Some performers are still courted by all sides. BBC1 Controller Lorraine Heggessey has said that chat show host Graham Norton is top of her wish list. He's currently under contract to C4, where his five-times-a-week programme delivered good ratings. Ironically, he was snatched by C4 from C5, after standing in for Jack Docherty on his talk show and winning a Bafta. It was only a matter of time before the other channels came calling with their cheque books.