The problem with wealth taxes is that they don't actually work very well

The bit of that recent Piketty magnum opus that had economists scratching their heads was his demand for a wealth tax. For it's a standard commonplace within the subject that you really don't want to tax capital. Doing so makes the future a great deal poorer than it could be. Just like that old windows tax made the future a lot darker than it needed to be. There's an opportunity to explain why in some numbers being attributed to the likely effect of Red Ed's mansion tax:

Mansion tax could wipe an average of 5pc off homes worth more than £2m should Labour win the next general election and make the proposals a reality.

The plans touted by the shadow chancellor, Ed Balls, could mean a 10pc drop for properties valued at £10m or more, and an 8pc fall for homes valued above £5m according to a new report from Savills.

The property group has also estimated a 6pc decline for those homes worth more than £3m.

People who own homes with a price tag above the £2m threshold could see their property value fall 4pc following Mr Balls' announcement that they will face a monthly levy of £250, a sum which gets progressively larger for more expensive properties.

£250 a month on a £2 million property is 0.15%. This drops the capital value of the asset under discussion by 5% or so. But the sort of wealth tax being demanded by Piketty is 1-2% annually, ten times larger than this tax. Now no, straight line predictions aren't all that good, there's changes in elasticity to consider, but it would be reasonable enough to think that a ten times the tax would have ten times the effect as a first stab at a guess.

So, in Piketty's desired world we'll be taxing wealth, or capital (they're rather the same thing) at 1.5% a year and thus the value of that capital, those bonds, stock and shares, that are being taxed will fall 50%. And that's why wealth taxes don't work very well. For consider the effect upon investment of a fall of 50% in the value of having made a successful investment.

It's still just as difficult to come up with a good business idea. It's still just as difficult to make that idea work, still just as expensive to make it do so. But the payoff from being one of the one in five that do manage to get something real going has just halved. Obviously, fewer people are going to make the effort and take the risks. Meaning that the future will be poorer by the lack of the effects of those new businesses that never were started.

Wealth taxes don't work very well for the simple reason that they make all our children poorer than they would have been even if they do make our children more equal. It's not a good bargain, not a good trade off.

The mansion tax is theft, a bit at a time

Labour's mansion tax was already starting to unravel even before Shadow Chancellor Ed Balls tried to save it with a few palliatives today. When you have left-wing Labour MP Diane Abbott complaining that the mansion tax would be little more than a tax on Londoners, and when other MPs and candidates nursing slim majorities are worrying that the tax might hit their own voters, and not just rich Tories, you know it's time to throw in the towel.

Strange, is it not, how politicians never ask how they could cut their own spending, but only think about how they can raise taxes from other people. Mr Balls reckons he can raise £1.2bn from the tax, which he says would come in handy for the NHS, he reckons (though the emerging black hole in the NHS budget is much larger than that). How does he know? He says much of the tax would come from foreigners with big houses in London, but does not seem to know how many of them there are. No, as usual, it will be the Great British public who foot most of the bill, and not just the rich. Tens of thousands of homes in London will be caught by it, for example, where the average price in a 'prime area' will probably hit the £2m mansion tax threshold by the time of the 2015 election. And 'prime' includes areas like Battersea and Clapham, not just swanky Kensington and Chelsea.

There are already plenty of taxes on property. Not only is there the council tax, but there is stamp duty when you buy a house and inheritance tax when you give it to your kids. Now the plan is to add another, of perhaps £4,000 a year.

We all know what will happen. The tax will be imposed on properties of £2m, and over the years, thanks to (politician-created) inflation and (politician-created) planning restrictions, the cost of property will rise. More and more properties will be hit by the 'mansion' tax (yes, including broom cupboards in Kensington), just as more and more people now pay the 40% higher rate of income tax, which was originally targeted at the wealthy but is now paid by people like teachers and police officers.

And our tax (and subsidy) system is already highly progressive. Wealthier people pay higher taxes of many kinds, while poorer areas get subsidies through the local government finance system.

The mansion tax is theft, a bit at a time. There will be many people who happen to live in large houses but have little or nothing in the way of income (such as those on pensions) with which to pay the tax. Perhaps the house was their childhood home and they can't face moving. Moving is a strain even for the most robust of us. Ed Balls says, well maybe poorer people could defer the tax until they sell the house or pass it on after their death. But that makes the tax even more complicated - it is going to need a means test and a lot of extra bureaucracy, more lines on the tax form and all the stuff that has already got us in such an overtaxed bureaucratic pickle. This is a tax we could well do without.