Imagine - and you'll probably have to - that you have a large six-figure salary and live in a ''1m+ house in London. You're hoping to buy a more prestigious place. And then the government raises stamp duty on ''2m houses to 7%. What do you do?

You could pay an extra ''40,000 for the privilege of living in a tatty terraced house or a dark two-bed maisonette in Chelsea.

Or you could decide that, if it's a big house you want, you should move out of London. In the civilized world, you can get a mansion with pool, tennis court and paddock for a little over a million - with the bonuses of increasing your chances of not having a complete cunt for a neighbour, and being within 15 minutes drive of one of the Britain's best music venues.

But of course, there's a problem. Unless you can work from home, moving to the civilized world requires some upheaval. If you're of a certain age, you might be able to retire early. You could sell your business a earlier than you intended. Or you could downshift and do consultancy work, popping into London only a few days a month.

And here's the thing. To the extent that people do this, their labour supply falls. Stamp duty can therefore 'deter effort' just like income tax can - maybe more so. This is because a tax on expensive items - given the foregoing we can hardly call it a tax on luxury goods - in effect reduces the returns to work, just as an income tax does.

The question is: how likely is this? Naturally, I'm biased, having made a similar move myself. But isn't at least possible? The notion that top rates of income tax have disincentive effects but higher stamp duty does not is, surely, very questionable.

Another thing: there is, of course, another effect here. As the smart money moves out of London, house prices there fall, thus imposing a cost onto their existing owners, but mitigating the cost to prospective buyers - thus transferring wealth from one sort of rich to another.