Mansion Tax: only the Lib Dems could think of something so dumb

The vagaries of the British housing market have thrown up many anomalies - one of which is that it has produced lots of people in London who are asset-rich but cash-poor. There was a time when having a house valued at £1million marked you out as being successful; now it seems it just points to a little luck over where you bought, and when.

The Lib Dems' "Mansion Tax" idea has been floating around for quite a while now. But like an undesirable in toilet bowl it just refuses to be disappear down the u-bend. I have a lot of time for Vince Cable but I don't know why he keeps pushing it. It's a truism that the more taxes you have, and the more complex they are, the harder they are to enforce. Especially when it happens to be so blatantly unfair.

The Lib Dems seem to have inherited the "eat the rich" moniker; except of course that only a fool or a knave would equate a £1m house with being rich. Or even being a "mansion". More like a town house in some parts of London. What if you bought 20 years ago and stuck around? What if you inherited it? What if you and a partner scraped together every penny you had, maxed out a mortgage and bought it for £200k only to see it rocket to £1m? Would there be a separate case for London? Or borough-by-borough?

Perhaps the part that shows how little this mad policy is thought through is the question of how to enforce it. Who decides what your house is worth? If the Lib Dems get their way it will be an army of quangos who have to snoop around - maybe even demanding entry. Well if it were my house and I thought the tax band inspectors were round I would strip out the furniture, fill it with kitsch, paint it violet and play the drums in the garden to annoy the neighbours. Then argue that the value of it has fallen through the floor. Simples.

People should be taxed because they're rich, not because their house is worth something. In fact people with smaller mortgages often have more cash.

Whenever I need cheering up I just tune in to watch the Lib Dems tie themselves in knots over what to do on almost any policy: NHS, students fees, foreign policy, taxation. They sold out to get into government and in the process have lost support from both the left and right. They're doomed, and this policy idea should be too.