Simon Jenkins writes in today's Guardian that it's strange that Vince Cable carries on talking about a mansion tax when we already have one, called the mansion tax:
England's property-based council tax stops at the present H-band. This means that the same tax is paid on all houses valued at more than £320,000 at 1991 prices (roughly £950,000 today). In parts of London, this means half the houses pay the same. Nick Clegg is right to protest that "it cannot be right that an oligarch in a £4 million palace in central London pays the same council tax as someone in a four-bedroom family home". It is ludicrous.
So what is the problem? The answer is no politician dares change it. All are cowards. They bid the rest of us to show spine, come to the mark, tighten our belts and take cuts without complaint. Yet faced with an equitable fiscal reform that could net billions in revenue, they cringe and whimper and protest it is all too hard. Like tackling drug illegality or the criminal justice system, politicians who think that something is politically toxic end up making it so.
Jenkins suggests that if the Liberal Democrats weren't cowards, they would introduce new tax bands, above band H, and charge increasing levels of council tax on them, "perhaps triggered at half-million pound steps".
But the real way we can tell that governments – not just the Lib Dems – are cowards is that, even aside from using council tax to introduce a mansion tax by proxy, they haven't even done the most basic housekeeping.
As Jenkins suggests, council tax bands are levied on the value of houses in 1991. If a rising tide floats all boats, then that's not too problematic – the most expensive houses in 1991 would still be in band H now, and the right people would be taxed the most. But it doesn't float all boats. Some houses have risen in value faster than the average, while some have risen in value less fast.
Despite this, there has never been a reassessment of council tax bands, and so many people are paying tax based on assets they do not actually have. Introducing higher tax bands without reassessing the existing houses would merely compound that error.
Doing so has nothing to do with raising revenue, and everything to do with basic fairness. If governments can't even bring themselves to do that, don't expect them to go much further with actually using council tax for good.