Where does London end: The city's boundary is defined by more than mere geography

You think it's easy, getting out of London? There is more than one answer to this question. It's not just a matter of sheer size, of having to work your way through the chaotic centre and the endless surburbs before you leave the city behind - it's knowing that you've left London at all. That's the hard part.

After all, how do you know when you've left London behind? The postal districts change? Fair enough, but then you end up in Richmond, Surrey, with a Twickenham postmark, and still have an 081 telephone number, that uniquely London dialling code. So you go beyond that, to the limits of the Metropolitan Police area of operations (that ought to do it) and you find yourself miles away, in Borehamwood, Harold Hill, Orpington or Epsom. But still with a London copper answering your 999 call.

In desperation, you fight your way to the ends of the Underground system: Amersham, Epping, Heathrow Airport, Terminal Four. And still you're in London - by definition: London Transport got you there. Clearly, you've still got miles to go. But even then, how far do you have to go before London becomes just another name on the map?

The thing is that London isn't just the name of a place, it is the name of a concept. And as such, it is highly portable. London implies a whole mass of notions, including service industry earning power, fee-paying schools, home ownership, London English pronunciation (and this includes Cockney, Mockney, Estuarial English, Sarf London, and Knightsbridge), a certain emphasis on food and drink, and most important of all, the recognition - spoken or implicit - that London town is the most important place in England, the place where anything that really matters is likely to happen. And wherever you find these values - and you find them all over the place - you find the idea of London brought into being like ectoplasm at a seance.

So away you go, still trying to escape the city's clutches. Kent? No, too many City stockbrokers and chartered accountants clustering around the tattered commuter stations of Sevenoaks and Tonbridge. Kent is a semi-rural retreat for London's financial community.

Surrey? The same as Kent, but substitute Guildford and Godalming, and not so quaint. Brighton? Seaside London dormitory, Bays-water with a shingle beach. The Cotswolds? Toytown weekend retreat. Maidenhead? Place for London spivs with motor cruisers on the Thames.

Henley? The same, but more self-fancying - and so convenient, thanks to Michael Heseltine's private motorway, the A321M. You can travel a good 50 miles in any direction and still you're in the London hegemony. It's all been annexed, one way or another.

It was the arrival of the fast electric railway, early this century, that really started this process. It became clear that how near or far you were from London was a matter of time, rather than distance; and that was that for London's outer suburbs, once rural retreats in their own right. The Eighties saw this in spades, with desperate mortgage millionaires scanning train timetables and motorway connections from Cirencester, Winchester, Cambridge, Marlborough, Bath even, anywhere faintly picturesque, to see if they could hack it into London in anything like two hours and be at their desks by nine.

The fact is that some of them went ahead and moved out, but so far from creating a cordon sanitaire between themselves and the city, only managed to spread London further and further away from Leicester Square or Marble Arch, or wherever the geographical heart of the metropolis is.

So how far are we now? At least 100 miles away? Doesn't it ever stop? Well, there comes a point at which even London starts to fizzle out, to be replaced by something else. Somewhere around Bristol, Cheltenham, Worcester, the Welsh Marches, the atmosphere changes.

It all looks pretty much the same as the Greater London of Hampshire, the Cotswolds and Suffolk - same chain stores, same scattering of fee-paying schools, similarly kempt, artificial countryside. But the gravitational pull of London is too weak and the pull of Bristol (or worse, Cardiff) is too great. It really doesn't make sense to think of London at this distance, and people don't.

London becomes a place which takes a whole day to get to and whose values might as well be those of Paris or Amsterdam. At the same time, the voices change. Everyone starts to talk Mummerset or Welsh and laughs at your funny London ways. You notice that your conventional Sarf London accent puts you in the minority, rather than the majority. They look at you in shops with a smile of bovine cunning and say: 'Yew from Lunnun, then?'

And if this is true for the West, it's even more true for the Midlands and the North. These are parts of the country whose entire heritage is based on their non-Londonness, the essentially anti-metropolitan viewpoint from which they see the world. It's not just that people from Northampton upwards don't share the London view, they actively don't want to. In fact, they hate London and all it means. What's more, it suddenly gets a lot colder when you cross the 52nd parallel, just to rub home how alien it all is up there. It's curious: moving south and west, London just seems to fray at the edges; but going north, it stops, quite abruptly. You've only got to look at a Midlander and they start ticking you off for being full of yourself.

My personal definition of Greater London is whatever is on pages six to nine, and 14 to 17, of the 1990 A to Z road atlas of Britain. A little crude, perhaps, but it works for me. I actually find it comforting, this great, sprawling hegemony; this feeling that I can travel for hours without ever quite leaving my home town. Indeed, I like the simplicity of an England reduced to great cultural blocs: London; the West Country (Mummerset, pixies, Dartmoor, clotted cream); and the North. It's modern. It's rational. And in the Europe of the future, the answer to the question, Where does London end? will be a doddle: it ends at Paris.

(Photograph omitted)