What is the good republican to make of this impending royal nuptial? Oh, that deep sinking of the heart. We are in for an avalanche of monarchalia. Tripe, tosh and trivia will dominate the press, rising to a climax as the deed is done: if only they'd quietly eloped to Gretna Green.

From now on there will be royal schmaltz by the bucket-load. And there will be faux moralising of hideous proportions: is it right ... is he/she to blame for the Diana tragedy... are this couple a proper moral example to the nation? And more impertinent balderdash of that kind. Then there will be absurd constitutional folderols about protocol and religion. Obscure academics will trundle out to obfuscate the finer points of constitutional and ecclesiastical propriety. This will be treated as if it were Henry VIII all over again - history repeated as farce. Nor is this 1937; imagine Tony Blair telling him to abdicate.

Good grief, monarchy-mania even broke out in the Guardian morning meeting yesterday, as one sentimental old soul called the Charles and Camilla saga the greatest love story ever told. Many guffaws. (But then this sentimentalist blew it by explaining why: Charles stuck to his beloved although she is a woman no man fancies, while rejecting the delectable Diana, every man's dream - loud boos all round.) I'm afraid we're in for a lot more of all that, not just in the bars where it belongs, but everywhere, for months to come.

The strongest argument for doing away with the royal family is just that - what it does to us, what it reduces us all to (including the obligation to write columns about it). If the idea of monarchy is that it confers pomp and circumstance, Bagehot's famous "dignified" bit of the constitution, the absolute reverse is the case. Ludicrous and grotesque for the wretched royal performers and their subjects alike, this is the least dignified of all state institutions. It always was, even in those relatively few reigns when the monarch did behave with due decorum.

The glittering emblem of the sovereign infantilises the nation into an unhealthy fascination with the doings of the royal household, children, servants, foibles and every banal saying and doing. It demeans the idea of citizenship and the meaning of the state. Why should these meaningless people be embedded in our national imagination?

Gossip is part of their role. Royalty requires a constitutional prurience in its marital doings, with its sole legitimacy drawn from a mostly fictional blood line. (I am not suggesting royal DNA testing, fun though that might be, but simply recalling how often the "blood line" has been broken in the divine succession.) Diana said she had done her duty and served her only purpose when she had produced "an heir and a spare". No doubt Camilla is not planning a quick trip to the IVF clinic in Rome that gives babies to the post-menopausal - but even the thought of it sends little constitutional shivers down the spine of experts on the Royal Marriages Act of 1772. All this is rather disgusting - and certainly not a dignified way of arriving at who should be head of state.

The tyranny of the monarchy is not in its puny temporal power but in its hold over the national imagination. Its spirit permeates politics, poisoning the appetite for reform and imbuing the nation with grandiose fantasies. It imparts an unsubtle taste for the thwack of "strong government" under the firm dictatorship of one party: Her Majesty's government. Proportional representation comes from another part of the brain, less hierarchical, less certain, more consensual - but somehow "not the British way". We have hierarchy hard-wired into us - tyrannical little kings and queens atop every pyramid of management.

The golden carriage keeps alive a heritage where half the globe is still painted pink and the sun never sets on our influence. The monarchy's link with an imperial past - how tight it clings to the commonwealth - encourages all our worst tendencies to strut self-importantly on the global stage: "punching above our weight" is the Foreign Office's perpetual forlorn endeavour. It helped to lead us astray on the road to Baghdad (but not Brussels).

The idea of our "ancient" line of kings infuses the way our politicians talk about the world. In security, trade, aid, spreading democracy or even the African scar on the global conscience, they always talk of "leading" whatever it is: look how we cling to our undeserved UN security council seat. These self-glorifying deceptions allow the British to imagine we can go it alone without Europe. The trappings of monarchy - we do ceremony so well - are the visible emblems of all this absurd delusion. It may be good for tourism, but stand and listen outside the gates of Buckingham Palace and you will hear American and other republican tourists sniggering at Ruritania, too.

So let her be Elizabeth the Last, and forget about whether Camilla is to queen it or not. If this Queen lasts as long as her mother, there is time to consider. If reform meant more to Blair than a little privatising, there would be a great constitutional convention after the election, to look at all the difficult questions now pressing. The Lords, the voting system, the West Lothian question (Scots ruling on English domestic matters) - and the monarchy. No more piecemeal constitution building on the backs of envelopes. Now is the right time.

Charles is not warmly embraced as future king. It doesn't help that his growing conservative meddling in everything from health to educational opportunity goes against the grain of progress. Nor does it help that he and his fiancee make a pointed political gesture in continuing to hunt, despite popular distaste. A Mori opinion poll two months ago asking people to choose between Charles or an elected head of state, found only 55% wanting him to inherit - an astonishingly narrow margin. Throughout the 80s and most of the 90s, the monarchy got more than 70% support. An ICM poll has found only 3% of under-30s identify with Prince Charles, and 59% of them wouldn't cross the road to see the Queen if she visited their town; 100% thought the royals should have just one palace.

If Charles had less of the death wish of his ancestor Charles I, he might have endeared himself by giving away much of his wealth, living simply and lecturing others to do likewise. Who better to castigate City boardrooms for their gross kleptocracy? His authority in talking to the rich would be considerably greater than his pontifications on a society he knows little of.