I was sitting in row Q of the stalls in the New Theatre in Cardiff on New Year's Eve when I realised that Britain was going to become a republic. We were not there to see Harold Pinter's latest play, nor some piece of left-wing misereria featuring a wrongly jailed Irishman, a venal politician, a corrupt newspaper tycoon and anal sex. Nor was the audience composed of professional middle classes seeking to be seared by indictments.

Entitled Jack and the Beanstalk, the play had an anonymous author, and though the leading male role (Jack) was taken by Su Pollard, this did not seem to be in pursuit of any challenge to sexual or gender stereotypes. In the seats around me were the engineers of Penarth, the garage owners of the Vale and the stolid burghers of Roath. And they and their children were all busy laughing at the Royal Family. At Camilla, at Fergie, at Diana, at Charles, at Andy, at the Queen Mum (crosses himself). Nor were these affectionate jokes, as told about erring friends or popular celebrities. They were contemptuous - cruel, even. These were jokes that were understood and responded to by the very people who might once have been expected to sustain monarchy.

So what? Previous monarchs have survived a mauling. Just look at the cartoons of Gillray, featuring farting Georges and fornicating Williams! But these are examples from pre-democratic history. Since universal suffrage, there has not been such a crisis of confidence in the monarchy - even at the time of the Abdication.

And today's crisis is not a simple product of infidelities, marital breakdown and a bit too much shopping. It is, rather, the exposure of the immense gulf in social attitudes and experience between the subject on the one hand, and the family from which the monarch has to be chosen, plus the gang of ridiculous aristos and celebrities with which that family chooses to surround itself, on the other.

My own moment of truth came with Prince Philip's views on gun control. It wasn't that I disagreed (though I did), but that his arguments had managed to be so utterly uninformed by the debate raging around him. In the circles in which the man moves, he simply hadn't heard the case being made for banning handguns. How could this happen?

If, like I was, you are tempted to write this off as a generational problem, consider how our future king is being brought up. He attends Eton College, where he mixes almost entirely with the nobs and the extremely wealthy. His idea of early adolescent joy is not to meet Alan Shearer or be given a season ticket for Manchester United, but to shoot a stag! I'm not necessarily against shooting stags (has to be done, old boy), but where's the fun in it? ("Daddy, did you see when the blood came spurting out of its head? Wasn't it ace?")

And now the heir to the throne is off in Klosters with Tara Palmer-Tomkinson, famous trust-fund babe. I have nothing against her - somebody has to model for Cartier and I suppose that it's never going to be me. But this is a woman whose magic moments come at events such as Countess Debbie von Bismarck's house-warming party in a converted police station in Chelsea, or when wearing turquoise python knee-boots. She is of the other-life, and yet she is important to William's view of the world.

On ITV this week, there will be a two-hour programme on the future of the monarchy, chaired (robustly, I hope) by Trevor Macdonald. Viewers will be invited to ring one of two 0891 numbers and cast their votes for or against the continuation of royal rule. This time, the royalists will win. But not, I suspect, for much longer. Twenty years from now, when asked "where is the monarchy?" the answer will resound around the islands: "It's behind us!"