Broadcasting: No one is indispensable, Michael - ask Barry, Des and Frank

Even the biggest names can suffer if they switch channels, warns Charlie Courtauld

Michael Parkinson's first chat show for ITV1 aired last night. The man who since his show began in 1971 is most associated with interviews on BBC1 follows the lead of some other notable defectors, many of whom have set precedents which he will be trying not to follow.

Michael Parkinson's first chat show for ITV1 aired last night. The man who since his show began in 1971 is most associated with interviews on BBC1 follows the lead of some other notable defectors, many of whom have set precedents which he will be trying not to follow.

Take Des Lynam. There were sackcloth and ashes aplenty in White City when the old smoothie of sport announced his intention to walk. After all, it was felt, Des is BBC Sport. But sport is bigger than Des alone, and four years on he's back, this time on Five Live, with his moustache between his legs.

Then there's Frank Skinner. Frank is one of those who obviously felt that his potential was unappreciated at his old home. So - with promises of his own chat show and the chance to pen his own sitcom - he was tempted to cross the waves. The fact that the chat show, Skinner, is dire and the sitcom, Shane, has been a critical flop only serves to confirm that the BBC had a point all along.

One of the biggest fears of any "irreplaceable" defector is that they suddenly discover that they aren't. When Barry Norman left the film buff's chair at the Beeb, he must have been as surprised as the viewers were when the vacancy was so smartly filled by Jonathan Ross, freshly poached from Channel 4. With his loud suits and louder opinions, Ross was - at first - considered too brash for the role. No longer, and it's Barry - stuck on the unwatched Sky One - who has been left feeling rueful.

So what's in it for the channels? After all, most of the big-name defectors turn out to bewhite elephants once they've been nabbed, making lacklustre programmes and failing to put their stamp on their new home. Spite for one, which shouldn't be underestimated as a TV motivator. What other explanation can there be, for example, in the BBC's decision to poach Graham Norton, than that it makes the Channel 4 controllers feel crummy. Before I've seen Norton's efforts for the BBC, I predict that it will lack the spontaneity and surprise that he achieved on So Graham Norton on Channel 4.

And what's in it for the stars themselves? Money, obviously, for one. If the experience leaves most presenters in tears, at least they're crying all the way to the bank. It's perhaps no surprise that the usual flow of defectors is from the poorer to the richer networks: Channel 4 to BBC, BBC to ITV or Sky. And those channel schmoozers make them feel so wanted, so important: until they sign on the dotted line, that is. Persuading a star to make that leap can do wonders for a channel boss's career. Witness how Michael Grade - the man who poached Bruce Forsyth back to BBC1 - has flourished since his triumph.

Arguably the most successful defections have been not in big-name stars, but in the field of political reporting. Both ITV's last political editor, John Sergeant, and their latest, Nick Robinson, learned the trade in the corporation's Millbank centre.

Maybe Parky can become one of those exceptions. Maybe he can flourish on ITV and prove the doubters wrong. Maybe he'll pull off some groundbreaking interviews. But I doubt it.