How the mansion tax will work, and who it will hit

If you're planning to own a mansion in the future, the tax isn't as bad as it seems…

Let's clear up one myth about the mansion tax straight away: it is not going to work the way Tim Montgomerie suggests in his Times column today. Montgomerie writes:

Last week Ed Miliband joined Nick Clegg in proposing a mansion tax so that the people who live in London’s parallel universe — many of whom come from overseas and pay little in the way of income taxes — might make a greater contribution. It was a perfectly reasonable intervention but, in a sign that the Conservative Party still hasn’t understood why it can’t win elections, many Tory MPs reacted with fury. Such a tax was, they complained, unfair on the person in a £2 million home who didn’t have the necessary £20,000 to spare.

A person with a £2m home would pay nothing in tax under any version of the mansion tax previously suggested. A £20,000 tax bill implies a house worth £4m. That's because the tax Miliband eventually produces is near certain to follow the same lines as the Lib Dems' desired tax, and be set at 1 per cent of the value of the home above £2m.

The reason why is obvious: if the tax was set at 1 per cent of the total value of any home above £2m, then there would be a huge incentive to depress, either artificially or actually, the value of the home. If your house was worth £2,010,000, it would be worth paying someone up to £10,000 to come round and do £10k worth of damage to it.

More practically, the lack of a cliff-edge at which the tax comes in is also likely to prevent it doing too much to property values. It will have a depressive effect, getting stronger as the house gets more valuable, and will likely knock quite a bit off the price of a £4m house. But the changes will be about pricing in the expected future cost of the tax to the sale price, not about avoidance. For much the same reason that no-body ever says "no thanks, I'd rather earn just £8,104 and not pay tax on my income", houses aren't going to start being sold at £1.99m in any real numbers.

But that example does reveal one of the bigger problems with the fairness of the tax. No, it's not the ridiculous example given by Toby Young of someone who finds themselves living in a £4m house without the money to pay the tax bill. If you can sell your house, buy a £2m one, and pocket the lifetime earnings of someone on the median wage as the difference, you do not really get to plead poverty.

Instead, it's that the vast majority of the incidence of the tax will be on the people who own the houses today. The depressive effect it will have on house prices will be pretty much instantaneous, and will then sit there forever. The tax will also slightly dampen the rate at which house prices above £2m increase — because every £100 increase in price imposes a £1-a-year increase in tax liability — but that is small fry compared to the initial hit.

That quirk explains why the suggestion of a tax provokes such vociferous outrage amongst those owning £2m+ houses. It really is unfair on them; but it's not a matter of unfairness against the rich, so much as unfairness against this generation of the rich. And really, for a government which has done so much to harm the cause of intergenerational fairness, that's a small hit in return.

Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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#Match4Lara: Lara has found her match, but the search for mixed-race donors isn't over

A UK blood cancer charity has seen an "unprecedented spike" in donors from mixed race and ethnic minority backgrounds since the campaign started. 

Lara Casalotti, the 24-year-old known round the world for her family's race to find her a stem cell donor, has found her match. As long as all goes ahead as planned, she will undergo a transplant in March.

Casalotti was diagnosed with acute myeloid leukaemia in December, and doctors predicted that she would need a stem cell transplant by April. As I wrote a few weeks ago, her Thai-Italian heritage was a stumbling block, both thanks to biology (successful donors tend to fit your racial profile), and the fact that mixed-race people only make up around 3 per cent of international stem cell registries. The number of non-mixed minorities is also relatively low. 

That's why Casalotti's family launched a high profile campaign in the US, Thailand, Italy and the US to encourage more people - especially those from mixed or minority backgrounds - to register. It worked: the family estimates that upwards of 20,000 people have signed up through the campaign in less than a month.

Anthony Nolan, the blood cancer charity, also reported an "unprecedented spike" of donors from black, Asian, ethcnic minority or mixed race backgrounds. At certain points in the campaign over half of those signing up were from these groups, the highest proportion ever seen by the charity. 

Interestingly, it's not particularly likely that the campaign found Casalotti her match. Patient confidentiality regulations protect the nationality and identity of the donor, but Emily Rosselli from Anthony Nolan tells me that most patients don't find their donors through individual campaigns: 

 It’s usually unlikely that an individual finds their own match through their own campaign purely because there are tens of thousands of tissue types out there and hundreds of people around the world joining donor registers every day (which currently stand at 26 million).

Though we can't know for sure, it's more likely that Casalotti's campaign will help scores of people from these backgrounds in future, as it has (and may continue to) increased donations from much-needed groups. To that end, the Match4Lara campaign is continuing: the family has said that drives and events over the next few weeks will go ahead. 

You can sign up to the registry in your country via the Match4Lara website here.

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.