On the canal bridge just behind Kings Cross, a policeman took a huge snowball full in the face and - I couldn't quite believe this was happening - giggled delightedly (it must have really hurt). His three colleagues gathered snowballs and pelted the mob of school boys and girls, quite sensibly avoiding head shots (think of the lawsuits). But they were outnumbered and outgunned. And anyway, they were easy targets, these coppers in their fluorescent jackets. And the school children, those alleged dysfunctional products of our greed-obsessed, low-serotonin, broken-homed, intolerably lardy, TV-ruined society, were in a snowy wonderland where there was no school, no rules and nothing to worry about. I've never seen London secondary school kids look filled to the brim with such girlish glee. "See if you can knock his helmet off," I yelled at one girl (which probably made me an accessory to something but I don't care: the delirium is infectious) and she pitched a curve ball that would have hit had the copper not ducked.

It's a scene one barely witnesses in London: one of innocence, albeit momentary; of snow in a city that doesn't do extremes of weather; of hostile battle lines suspended and replaced - just for the day - by playful ones; of gratuitous wonders that fall from the sky and blindside you. Yesterday, London was filled with such wonders. The headline said: -5C and we're all going snowhere. Yesterday, London went on a trip to snowhere, which sounds like oblivion, but is infinitely nicer.

That sound snow makes as it packs under your boots! The velvety swish of car tyres on untreated side streets! That numinous glow that greets you as you open the curtains and realise that even though it's Monday, you are quite looking forward to walking to work, especially if you can make a snowman with strangers you meet on your journey! The way your fingers swell after throwing snowballs while wearing functionally useless woollen gloves! (We need poets to invent names for all these things and write sonnet cycles to their joys). And, above all, the snow's silencing of the great roar of London: usually, I keep my iPod on as I walk to silence London's racket: yesterday I didn't want to. Every side street I strolled down yesterday offered - if this doesn't sound too pretentious in a Karen Carpenter-meets-Immanuel Kant kind of way, which I know it does - an unexpectedly sublime kind of hush.

Yes, yes, I know so far this article this sounds a little like those photos of the Notting Hill carnival, with a white policeman dancing with a nice old Caribbean lady. A deluded paean to an interlude that misses what the real London is like, with its quotidian meanness, stabbings, lonely deaths, rapes, intolerance, greed and woe. But, just for a moment, cram your cynicism and yield, as London did yesterday, to the seduction of snow.

Other cities - Winnipeg, say, Moscow or Bergen - cope with snow, subdue it and go to work through impeccably gritted roads. London isn't like that: it rarely copes with anything; these days, it masters nothing. Equipped with a loveably tragi-comic public transport system, our capital fails on a daily basis. The poor suckers who live here get - at best - inured to this hopelessness. Yesterday London was so hobbled by the snow that the situation was even worse than hopeless: usually six million Londoners get to work by bus; yesterday there were no buses; the tube was even more spectacularly unreliable than usual. Even gnarly cyclists in all kinds of crypto-pervy winterwear were laid low (the nameless gent who I helped back on to his bike on Mecklenburgh Square after a comic slo-mo tumble really should have left his wheels under the stairs). Just for a day Londoners got hit by something special.

For a day at least, Londoners returned to a forgotten innocence. Yesterday the headlines howled about how £2bn would be lost yesterday thanks to public transport disruption. Two words: So. What. We're in the middle of a credit crunch and £2bn is the sort of money a hedge-fund trader might find in the lining of his Armani suit. Yesterday we stopped measuring our lives in coffee spoons, overdrafts and balance of payments deficits. It felt good.

We needed the snow to remind us of that innocence. We needed it to remind us of who we are. We are not just homo-economicus, we can't be defined by the size of our negative equity, the burden of our personal debt, or numbers of en-suites. We need something more this winter than cowering at home noting down how many times Gordon Ramsay swears on Channel 4. Our new year resolutions are broken, our jobs insecure, our pensions worthless, our spirits crushed by January's post-Christmas gloom. We needed something to lift our spirits, to give us the excuse to play to no discernible economic benefit.

And yesterday here it came, free as air, falling on to my bare head as I walked down the canal towpath. I was doing what a human being should do now and again: stare. A Spanish man and I watched a heron dive from the ice into water that is starless and bible black. Would it ever resurface? What could it find down there to eat? We did what London hardly ever allows: exchanged the conspiratorial glances and then resumed the satisfyingly economically unproductive business of staring.

In London, this doesn't happen often. We trust our dour reflexive, self-poisoning moaning as a lifestyle philosophy instead. We like it that way: strangers are strange and Britain, damn everything about it, doesn't work. Why don't the buses run on time? Why are we so hopeless? Why can't something be done (usually by someone else who we can blame for their shortcomings)? And this chorus of self-immolation is taken up countrywide: why, non-Londoners ask, is the capital brought to a standstill by a little snow? Why can't you southern ponces get your act together? And the cry is international too: as I walk through the St Pancras Eurostar terminal, a French couple consulting the warnings about the tube, roll their eyes as one. He said: "Typiquement anglais. Rien ne va plus!" They both laugh, as if to say their Gallic expectations had been confirmed.

And so we surrendered to delight. We found better questions to ask: how do you roll a snowman? Where the devil are my galoshes? What have you done with my sledge? Can one get to work by sleigh? Doesn't Prokofiev sound lovely when it's snowing outside? After leaving the canal, I walked down through virgin snow in quiet back streets nestling right next to the Eurostar train line. A snowy bucolic idyll at the heart of the metropolis. I looked from Camley Street through the snow to the gothic tower of St Pancras - a Caspar David Friedrich painting had suddenly leapt before my eyes.

Over on Tottenham Court Road, there was slush and crowds bustling. Here people were shopping and barking into mobiles, like they do every day. So I took the tube up to Hampstead. I remember an old cartoon depicting gents with handlebar moustaches and ladies in thick bloomers tobogganing (we don't use this word often enough) in Parliament Hill Fields, above the caption "Les Pistes d'Hampstead". I wanted to find out if these legendary pistes still exist. A voice on the tube PA announced: "Due to adverse weather conditions [I think she meant snow, which is not adverse to my borderline hysterical sensibility] there will be delays on the Northern Line." Nobody on the platform batted an eyelid, except for one guy who said: "Delays on the Northern Line, eh. How very unusual". A ripple of giggles passed down the platform. At Hampstead, the lift that took us from the stygian depths to the winter wonderland was filled with giggling students. Everyone was jaunty, striking up conversations with strangers.

As I walked towards Hampstead Heath, I heard whoops and cheers. The heath was like Narnia (though with none of CS Lewis's unwonted Christian allegorising). My God, I told myself as I walked through a heavenly avenue with snow-laden branches bejewelling my steps, this is the most beautiful city in the world! (I was delirious, high on pheromones, snow bonkers, and in need of a good slap).

I stand on Kite Hill, looking across the London panorama below and remember the ending of Joyce's The Dead. "His soul swooned slowly as he heard the snow falling faintly through the universe and faintly falling, like the descent of their last end, upon all the living and the dead." My soul was swooning (there, I admit it) yesterday as I stood and saw the snow falling, not on Joyce's Ireland, but on dirty old London, reborn as a thing of beauty. It was snowing from Epping Forest to Heathrow, Upminster to Uxbridge, on duke and dustman in a way that it hasn't for ages and probably won't for a good while. Savour it, I told myself.