Seen from Labour's backbenches, a mansion tax must seem an easy way of soaking the rich while sparing the ordinary working people of whom they claim to be so enamoured.

No wonder the snatch-and-grab brigade are salivating. But the property market is too complicated for such a crude measure to stand a chance of working.

It would, in reality, have myriad damaging effects. How, for starters, would Labour set about valuing properties? Where would they find the army of surveyors required, and how much would that cost?

How would they deal with the inevitable appeals against over-valuation? Would they take into account whether or not a house was mortgaged or owned outright?

And what about elderly widows, say, who are asset-rich but cash-poor and simply cannot pay? Sending grannies to jail is not a good look.

Taxes change the behaviour of both buyers and sellers - and the housing market is extremely sensitive.

A levy on properties worth more than £2million would put an effective ceiling on valuations.

The Chancellor should tackle bloated welfare spending, curb public-sector waste and introduce measures to get more than nine million economically inactive people back to work, instead of introducing a mansion tax

Who wants to pay £2.1million if that means a hefty tax bill for the privilege? It is a grotesque interference in what should be a free market.

Cack-handed attempts to hit homeowners help no one. They create distortions and make genuine problems even worse.

Lord Mervyn King hit the nail on the head when he pointed out yesterday that property is already subject to a cats-cradle of taxes.

Homebuyers and sellers must navigate stamp duty, council tax, capital gains tax and inheritance tax. The last thing we need is yet another levy.

As one of the most distinguished former Governors of the Bank of England, Lord King knows what he is talking about.

Lord Mervyn King hit the nail on the head when he pointed out yesterday that property is already subject to a cats-cradle of taxes

Which is more than can be said about the Chancellor, who has made rather exaggerated boasts about her own, less-impressive time at the Bank.

Taken along with other measures, including extending the grasp of inheritance tax and VAT on private school fees, a tax on higher-value properties looks vindictive and anti-aspiration.

It will be a blow for the property market, further depressing it at a time when confidence is already fragile thanks to Labour's mis-handling of the economy.

Yes, the Chancellor does need to find some way to fill the black hole in the public finances.

But she should tackle bloated welfare spending, curb public-sector waste and introduce measures to get more than nine million economically inactive people back to work.

A mansion tax is not only nasty and vengeful - it will be self-defeating.

A mansion tax is not only nasty and vengeful, it is self-defeating