Miles Kington: Why comedians won't make fun of Mr Birt

'Give what's his name, John Birt, a ring - he can come round and have a look at it. He's in the Yellow Pages'

When Tony Blair loses credibility and is finally thrown out on the junk heap of history, or whatever the House of Lords is called by then, we will all look back and wonder where we, personally, began to lose faith in him. If we never had faith in him in the first place, we will just wonder when it was that we became really, really impatient with him. In my case, it will be when he started hiring John Birt as an odd job man.

It is quite easy to think of John Birt as a handyman in the sense that, although he doesn't seem to be very handy at anything, he is always available. So when someone says to Tony Blair, "Blimey, Tony, I think crime needs fixing, we ought to get someone in to look at it", Blair says, "Give what's his name, John Birt, a ring – he can come round and have a look at it. He's in the Yellow Pages. I'll leave you to handle that; I've got to fly off and bring universal peace...."

Quite why Tony Blair thinks John Birt is a good odd job man is unclear, as nobody can ever think of anything that John Birt has fixed to anyone's satisfaction. His defenders say that he brought some much-needed reforms to the BBC, and they may be right, but while working in and around the BBC during the Birt years, all I ever sensed was that he brought fear and conformity to the place, crushed a lot of enterprise and initiative, sold off many of the best assets, and became hated throughout the organisation except among his clones and favourites. If he also brought in much-needed reforms, they would have had to have been miraculous to outweigh the harm he did.

But what has happened to John Birt in the last few weeks is something I hadn't quite expected. He has become a figure of fun. Tony Blair has hired him for so many odd jobs that it has become clear that he isn't making much of a mark in any of them, and when it was noised abroad that he was going to be given a brief to sort the railways out, people didn't even bother to laugh. They just raised their eyebrows and snorted in derision. Normally people in the comedy business would start making bad jokes about him introducing "conductor choice", and having a quota of independent train drivers, and being worried about rush hour ratings, but nobody in the trade, as far as I know, has even bothered to make jokes about John Birt.

Outside the trade, it's slightly different. On Broadcasting House on Radio 4 yesterday they asked listeners to come up with satirical suggestions on how to employ John Birt meaningfully. In The Independent last week, when Julian Barnes was asked questions by readers, he made two very rude remarks about John Birt even though none of the questioners had mentioned him. What this all means is that we are at that magic moment when a public figure undergoes an amazing transformation into a public figure of fun.

Usually we only notice this some time after the deed. I cannot, looking back, pinpoint any particular moment when Paul Gascoigne went from being a hero to being a buffoon, or Jeffrey Archer finally lost people's respect and gained their jeers. I think there must have been a moment when Chris Evans went from being a person who earned laughter to a person who deserved to be laughed at, but as I could never summon up any interest in him on any level, I didn't spot it. It sort of happened to Peter Mandelson. People have tried to do it to John Prescott and it might have happened to Keith Vaz, if anyone knew where he was.

Occasionally it happens the other way round and figures of fun become heroes. It has happened recently with David Beckham. For some reason I could never quite pin down, Beckham became a byword for stupidity, along with his wife, Victoria. Folk jokes started circulating about things that Beckham might have said. As Irish comedian Ed Byrne said on television once, "We are all incredibly grateful to David Beckham. It's because of him that the English have stopped making jokes about the Irish." And then, when he scored his super-goal against the Greeks and kept the English in the World Cup, and when he turned out to be rather a good captain, it all changed and people stopped making fun of him and started giving him respect.

As an afterthought, the thing I couldn't help noticing about the treatment Birt got on Radio 4 yesterday was that nobody called him Lord Birt. It was either John Birt or Mr Birt. The last time I noticed someone's title being tacitly dropped was when Lord Archer re-emerged as Jeffrey Archer.