Christmas wouldn't be Christmas without the Archbishop of Canterbury, or similar, telling us that Christmas doesn't really have much to do with Christmas. The ritual is as reliable now as the Today programme helping us into the drunken mood by explaining that drunks sometimes fail to grasp the true meaning of the Watchnight Service. It's traditional, like the heartwarming urban myths of "PC councils" and "Winterval". Like the old tales told by jolly red-nosed journalists of Santa's sleigh being banned on "health and safety grounds". Like someone saintly asking how the filthy secularist Richard Dawkins can dare to sing carols. Or like the leader of a British political party admitting shyly that, no offence, God doesn't get even a single transferable vote in his universe.

Actually, the last part is a novelty. Nick Clegg made no fuss about it in an interview last week. He did not "seek to impose his view", he was not talking about Christmas, and he was respectful in his remarks on religious faith. Perhaps because he is the very model of a modern major Liberal, he has even committed himself to raising his children as Catholics. But we'll get to remarkable contradictions shortly.

The latest leader of the third Westminster party is an unbeliever, or at least a firm Don't Know. In a country that flays itself - or do I mean stuffs itself? - each December with angst over the flight from God, this is new. Possibly refreshing.

Britain is not the US, obviously enough. We do not expect those we elect to pray for, with, over, or through us. Indeed, in one of his recent valedictory TV interviews, Tony Blair suggested that our politicians are given short shrift if they appear to flaunt faith. Under his leadership and Alastair Campbell's direction, new Labour famously did not "do" religion for this very reason.

The former prime minister may have misunderstood a nuance, however. Faith is respected in Britain, if not adhered to. The distinction we make is between a man with private beliefs and a man capable of hinting that the Almighty is his personal missile guidance system. Uncontroversial religious adherence without ostentation or the whiff of delusion is taken for granted. In a politician, it is expected. Hence the faint surprise at Clegg's admission.

Politicians are supposed to inhabit the myth of the normal. It renders them mostly white, mostly male, mostly straight, and mostly Christian: "mainstream". Blair's inhibitions over his covert Catholicism may have stemmed, in fact, from a spin doctor's suspicion that even an attachment to a non-Established version of the dominant cult was a bit risky, politically.

Does it still matter in this country if a party leader is publicly none-of-the-above? In America, such a declaration would be political death, a blogging at the stake, a media stoning. Despite every guarantee in the constitution, secular politics is impossible. We are not that mad, or not yet. But if Blair kept even his Catholic leanings to himself for fear of the consequences, where does that leave the polite agnostic-atheist of Liberalism?

Back to the Archbishop of Canterbury, drunks, PC councils, hacks, heathens and unbelievers. If you have no religion, you have to love the modern British Christmas, for one reason alone. It confuses the hell out of those who claim the festival as their own. It is the best example of humanity's ability to detach itself from received belief, to reject, reinvent or, if you will, thoroughly distort and debase an uncongenial message. Good Christians hate the modern, bloated public Christmas. And they are, by their non-twinkling lights, quite right. It's a travesty.

It is a travesty, nonetheless, embraced by a majority still liable to claim, when push comes to shove, that they are good Christians. Secularism, materialism and all the other unconvinced "isms" did not sully the purity of the original chaste and simple Christmas message. Professing Christians, believers basting themselves in excuses at the check-out and the bar, did that.

God and the infant and the spirit are afterthoughts - OK, a single afterthought: weird - come mid-December. Gluttony and Mammon are altogether more popular, yet their devotees profess religious faith. With no sense of irony, they also complain about gluttony and greed. You can't pin that one on Richard Dawkins, I think. Those who claim to have beliefs don't seem to care much about belief. There is hope yet, then, for Nick Clegg. Christmas is a time of hope, after all.

From the outside looking in, in any case, it often seems that God's messengers fumble their lines. It is probably not for me to say, but is Dr Rowan Williams helping the cause when he picks this time of year to dismiss the Three Wise Men as "legend"? To summarise Cantab, but only slightly: not necessarily wise, or kings, or men, or a trio. That nativity play and all those shining little faces? A waste of time. The gift-bearers might as well have been Jedi knights.

As a history lesson, all of this is no doubt excellent. The trouble for God's party is two-fold, or triune. First, if you begin to pick holes in the Biblical-historical record it is difficult to stop. You could easily end up throwing out the baby with the manger straw. You might be left with a God-shaped notion, of sorts, but why would it be a Christian, far less an Anglican, notion?

Secondly, whatever happened to the mystery of faith? A belief in the probably-not is beyond some of us, but a leap in the dark, a bungee jump in the direction of myth or an immanent truth, is supposed to be in Williams's job description.

Finally, it is all very well to lecture Radio Five's Simon Mayo and Ricky Gervais (God help someone) on the foundations of faith, but hasn't the archbishop stopped to notice some of the other things people are believing these days? It's a competitive market out there. There are even convinced atheists who are none too sure about the existence of Richard Dawkins. But we know that the tale of the Three Wise Men is excellent hokum. Or at least no worse than the rest.

How is a religion maintained when a story told to children for centuries is discarded, just like that, by a jolly old man with a big white beard who wears funny robes? Santa Claus wouldn't give up so easily. Williams seems to forget that children do not, in fact, do theology; they do faith, for a while at least The child in the tale of the non-existent Three Wise Guys later had something to say about that. Canterbury reminds us that some grown Christians are, in fact, unbelievable.

More believable than the LibDems, obviously. Nick Clegg should realise, if he doesn't know it already, that he won't get my vote just by embracing reason. The Christians won't get Christmas back just by conceding that certain narrative strands are fragile. So what remains?

Probably just the old pot-pourri of hope, doubt, half-digested belief, naked fear and fellow-feeling. And too much food. It is safe, now, for a politician in this country to hope for a career without hoping for an afterlife. It is safe for a man of God just to have faith in the possibility of belief, rather than possess belief itself. It is safe just to look for a little light in the winter darkness wherever you can find it.

Is Christmas bigger than Jesus? The sainted Lennon of Scouse has given me no instructions on the question. It's his song I keep hearing in the supermarket, though, over and over and over. God should probably take the next fortnight off, like most people. Or spend it among those who need and want His company. We could call that a Christmas truce, then watch the football. It's traditional.