How do you put a genie back in the bottle? With macroprudential regulation, of course. Chancellor George Osborne is wrestling with a genie of his own making in the form of Help to Buy.
Today he has announced more tools for the Bank of England to manage the housing market.
The scheme, as we have reported many times, provides up to 20 per cent of the cost of a new build house or, from January, a guarantee (from the government to lenders) allowing buyers to put down only a five per cent deposit on any property, whether new or old.
It's a generous boost for buyers and seemed a good idea when it was introduced but very quickly the market has improved in some parts of the country.
Nationwide reports house prices in the UK as a whole are up five per cent compared with a year ago and have rocketed ten per cent in London over the same period. In fact, London houses are now eight per cent higher than the pre-crash peak of 2007.
That has led many to fret there may be a bubble in the making, in the South East at least.
The Bank's new Financial Policy Committee (charged with macro-prudential genie-wrestling) said this week it was "vigilant" to the threat posed, although it didn't see one yet, and that prompted the chancellor to act today.
Help to Buy was always intended to be a temporary, three-year scheme but the Bank will now be asked its view every September whether it should be continued in its current form or be adapted to the conditions of the time.
It could recommend that the fees charged to commercial banks for the government's guarantee be raised - which would slowly turn the taps off for borrowers - or it could lower the maximum price eligible from £600,000.
I understand these are just examples of what the Bank could recommend and, indeed the FPC can recommend stiffer lending criteria like lower loan-to-value ratios (i.e higher deposits from buyers) and tougher affordability tests.
So far, so good, but what concerns me is how the authorities manage the dramatic variation in the housing market in Britain.
While London booms, property inother parts of the country is still far below the peak of 2007 - if you bought a house in Northern Ireland just before the crash, I'm afraid you're still looking at a 52 per cent loss.
No one, it seems, is specifically charged with acting to stop a regional property bubble. Curbing Help to Buy might temper some of the forces but it's unclear to me what other actions might be taken.
Now where's a genie with three wishes when you want one?