The selection of Kate Middleton, a lowly commoner drawn from the very dregs of society, as Prince William's bride has been the subject of great speculation, much of it thinly veiled snobbery. But Britain is broken. Social mobility is at a historic low, state education and public healthcare are in crisis, and our own prime minister has blamed the truculent immigrant and his concealed wife for our lack of national cohesion. Once upon a time, royal marriages were political acts that forged links between different nations. Instead, William and Kate's wedding will bind this nation to itself, and in marrying so very far beneath himself, I believe the young prince has made a heroic and deliberate sacrifice to achieve this end.

Pause for a moment. Imagine being Prince William. Imagine knowing that the best justification most rational people could come up with for your heavily subsidised existence was that you were a symbolic figure. And symbolic of what, the boy must wonder. History? The land? The nation itself? A notion of refined nobility? Grace under pressure? Or perhaps some abstract idea of temporal continuity? Unable to escape being a symbolic figure, the prince's recent activities suggest he has chosen instead to embrace the role in the most profound way imaginable. And, I believe, this is why the wedding of Prince William and Kate Middleton itself seems symbolic on an admirable and unprecedented level.

Jessie L Weston's 1920 study of Holy Grail mythology, From Ritual to Romance, pictures Britain as a wasteland, an image appropriated by TS Eliot to describe the aftermath of the first world war. The Fisher King must search the devastated terrain for the Holy Grail, and drink from it to heal the land. Broken Britain is that wasted land. William is that Fisher King. Kate Middleton is that lovely grail, full not of the blood of the crucified Christ, but of the blood of the Middletons, who run a children's partyware business in Berkshire. And Kate's wedding to wise William is a ritual that may help to fix what David Cameron's vision of the Big Society so far has not. For in choosing Kate, a simple girl from a school near Swindon, as his bride, William is in fact taking each and every British subject – man, woman, old, young, black, white, Christian and Muslim – into his royal bed, and binding us all to each other in the white heat of his princely passion.

Kate was educated at Marlborough College in Wiltshire. It is a private school, yes, but it is no Eton, and its most famous alumni are little more than flannelled fools: the comedian Jack Whitehall, the children's author Lauren Child, and the pop musician Chris de Burgh, whose 1976 Christmas hit A Spaceman Came Travelling describes an alien being's disappointment in the shortcomings of human society – disappointments it appears William shares, and is trying to address in his own esoteric way. But his motives for plucking a bride from such an inauspicious establishment are, I believe, twofold, and we must admire and accept the occult reasoning behind his selfless choice.

First of all, Marlborough College, where Kate Middleton flushed into womanhood, is set in a magical landscape that has been declared a world heritage site, being only five miles from the exact centre of the Avebury stone circle. Perhaps Kate's growing body absorbed the magical energies of the region. Perhaps it did not. It does not matter. She is from, and she is of, the ancient wetland. The arrangement of the 6,000-year-old circle, and the stone rows, burial chambers and mounds that surround it, is explicitly symbolic, explicitly sexual and explicitly ritualistic, and as such it shares the same transformative agenda as Friday's royal wedding.

In Avebury, the West Kennet Avenue, a long row of erotically paired stones, uncoils snake-like from the circle, as if to penetrate nearby Silbury Hill, a fecund 37-metre-high female belly, which rises from the marsh to meet it. The prince has taken his lowly bride from within this charged landscape, where our ancestors celebrated the union of man and woman in stone and earth, and began the communal processes that forged a nation from their descendents, the broken nation that William the Fisher King must now heal. Our shaman-prince could not have chosen a better receptacle for his magical purposes than Kate Middleton, a peasant-spawned serf-girl, sodden with the primordial mire of the Swindon-shadowed swamplands.

Secondly, in choosing a commoner for his bride, William gives hope to millions of socially disenfranchised Britons. Only two Tory generations ago, the prime minister Margaret Thatcher was proud to proclaim herself "a grocer's daughter". A mere 20 years since she passed power on to John Major, a garden gnome salesman with six O-levels, it is impossible to imagine either in government today, composed, as it is, principally of former members of the elite Oxford vomiting society the Bullingdon Club. The state-schools system is stretched to the limit; the withdrawal of further education grants deters poorer students; and government contributions to the Bookstart scheme, which gives books to children who might otherwise have none, have been halved. It is not possible to imagine a Thatcher ever getting out of Lincolnshire today, let alone becoming prime minister.

But in snatching Kate from the gutter, William stooped even lower than he would have done had he chosen Margaret Thatcher for his bride. Kate's parents aren't even grocers. They sell novelty hats and paper plates. It's no coincidence that as genuine social mobility in broken Britain is eroded, so commoners turn to the National Lottery, The X Factor and Britain's Got Talent. Winning them represents the only chance real people have to change their circumstances significantly. It could be you. And, like some giant illuminated penis flying over the rooftops of suburban homes and frothing at random passing women, William has pointed himself at Kate Middleton, the Susan Boyle of social mobility. In declaring her his princess, he brings hope of real change to millions of people denied a decent education and the means to better themselves, to millions of tiny babies denied even books, that one day they too could be randomly rewarded with untold wealth and privilege.

The wedding of my wife and I was a small affair, with 40 or so guests. We were not required to arrange our day along magical or symbolic lines, though admittedly some aspects of the Catholic wedding ceremony confused me, and my wife is yet to explain the tradition whereby I have been obliged ever since to sleep alone each night on the toilet. But as a symbolic figure, poor Prince William's wedding is hostage to political expediency. Consider the faces he will see as he and Kate make their solemn vows.

From the world of government, the prime minister and Mrs David Cameron, and the deputy prime minister and Ms Miriam González Durántez, holding whichever suit the prime minister has chosen not to wear; from the faith communities, the Reverend Gregorius, Anil Bhanot, Malcolm Deeboo of the Zoroastrians, The Venerable Bogoda Seelawimala Nayaka Thera, Obi-Wan Kenobi, Optimus Prime, Yog-Sothoth, Captain Marvel and Cardinal Cormac Murphy-O'Connor; and from the twin spheres of entertainment and sport, Mr Ben Fogle, Mr David Beckham and Mrs David Beckham, Mr Madonna Louise Ciccone, and Sir Elton Hercules John and Mr Sir Elton Hercules John. Candles in the wind all.

But as he gazes at this golden shower of dignitaries, it is William who will have the last guffaw. He knows that this was not so much a wedding as a psychic rescue operation, a healing ritual for broken Britain, a pantomime of hope for the terminally hopeless. In taking Kate Middleton as his bride, Prince William, more than anyone in any position of power in Britain today, has tried at least to do something to help. I hope sincerely that both of them are very happy.

• Stewart Lee's Comedy Vehicle starts on BBC2 on Wednesday, 11.20pm. A series of events called Stewart Lee's Austerity Binge starts at the Southbank Centre on 27 May. He is among artists performing John Cage's Indeterminacy in a short season he's programmed for the Cheltenham Jazz festival.