NEW YORK may have a reputation as a brusque, unfriendly place, but to those who buy expensive properties, at least, it can be very welcoming. Take the anonymous owner of the penthouse in Midtown Manhattan’s 90-storey One57 skyscraper. The flat sold for $100m in December, a New York record. The city collected a modest $2.8m in taxes, 2.8% of the price, when the deal went through. And the new owner’s first annual property-tax bill came to $17,268, just 0.02% of its value.

In contrast, if Britain’s main political parties can agree on anything, it is that expensive homes in London should be taxed heavily. In 2009 Vince Cable, a senior Liberal Democrat, first proposed a “mansion tax” on residences worth over £1m ($1.6m). Five years later Ed Balls, then Labour’s shadow chancellor, said he aimed to raise £1.2 billion a year from a similar policy. Not to be outdone, last December George Osborne, the Conservative chancellor, raised stamp duty, a levy on property purchases, for houses worth more than £1.13m. A hefty 12% of the portion of the sales price above £1.5m now goes straight into the government’s coffers.

So does that make New York a property-tax haven, and London a den of expropriation? Not exactly. In fact, it is New Yorkers who pay more tax on their property overall: last year New York’s 3.5m households coughed up $12 billion on homes worth $1.7 trillion, a rate of 0.71%. In contrast, London’s 3.5m households paid $11 billion last year on property that would sell for $2.2 trillion, just 0.51% of its value. London’s take is lower for a heartening reason: it is only expensive properties that it taxes heavily, whereas New York soaks the poor.

Around 40% of New York’s $50 billion a year in tax revenue comes from property. The city charges fixed rates on the assessed value of every home within its borders. In buildings with more than three units, state law requires flats to be valued at a multiple of the rent they could fetch if let out. This anodyne-sounding rule is tantamount to a massive tax break for the super-rich. Because stratospherically priced flats are rarely let out, there are no comparable properties in the rental market. That forces the taxman to rely on much more modest homes instead, leading to ludicrous valuations: although the penthouse at One57 cost $100m, it was valued at $6.5m.

Another quirk of New York law further shields the rich. In order to protect homeowners from soaring liabilities in the event that their properties appreciate faster than their incomes do, the city has instituted caps that limit tax increases for some types of buildings to 6-8% a year and 20-30% over five years. This system shifts the tax burden away from areas of sharply rising values and onto blighted regions where prices are stagnant. As a result of these policies, New York’s property-tax system is sharply regressive: the cheapest homes, ranging from $100,000 to $250,000, tend to pay the highest rate (1.08% on average in 2014), whereas those worth more than $10m get away with just 0.36% (see chart).

Property taxes in London, in contrast, are reasonably progressive. Although the annual levy on the value of British homes, called council tax, is even more biased in favour of the rich than New York’s is, it accounts for a far smaller share of the local property-tax burden. Instead, stamp duty brings in 45% of the total (in New York, transaction taxes represent just 13%). And thanks largely to Mr Osborne’s recent reforms, stamp duty falls most heavily on the rich. The more expensive a house gets, the higher the effective tax rate.

Mr Osborne has also introduced a new levy to thwart loophole-seekers. Before 2012 Britain did not charge stamp duty on properties bought by companies rather than individuals. Now, such residences not only incur the highest duty of all, at 15%, but are also subject to a separate, new annual tax on their value. In the year to April 2015, this policy raised an estimated £104m in London, increasing total property-tax revenues in the city by 1.6%.

Together, these reforms have shifted the burden of London’s property taxes much more heavily onto the wealthy. Under the old rules, the 1,400 residences in London worth more than £10m were taxed at just 0.61% of their value. The new rules increase this to 1.09%, three times what homes of that value pay in New York. Meanwhile, Londoners living in properties worth less than £1m paid 0.44% last year, less than half the rate in New York.

In addition to its progressivity, London’s system also trumps New York’s on consistency. Although council-tax rates vary among London’s 33 boroughs, the maximum bill is just £3,356 a year. As a result, liabilities for expensive homes stem mostly from stamp duty and from the tax on property owned by companies, for which units of equal value always pay the same amount. That is in sharp contrast to New York’s tax code, which is riddled with exemptions that enable some homeowners to dodge the taxman almost entirely.

In 1971, after decades of population decline in Manhattan, New York launched a scheme to attract residents by offering a subsidy to developers intended to benefit homebuyers. This system, known as 421a, slashes property taxes for 10-25 years after a new development is built, in exchange for promises to build affordable housing. As home values have risen, these abatements have proven far costlier than expected: today, they add up to $1.1 billion a year, or 2% of New York’s total tax take.

Worse, the programme has complicated rules on eligibility, which are only worth bothering with for big or pricey developments. Just 153,000 homes—among them One57—benefit from it. Even within this group, the magnitude of the benefit varies widely, depending on whether a building is near the start or end of its abatement. As a result, among homes in New York worth more than $10m, the most heavily taxed fifth pay three times as much in annual levies as the most fortunate fifth.

Just 12,750 of the 153,000 homes receiving a 421a subsidy were classed as affordable in 2013, according to the Association for Neighbourhood Housing Development, a trade group. At $400,000 a unit, the city could build that many affordable flats itself in less than five years using the money it spends on 421a. The tax breaks offered under the scheme, in contrast, can last five times longer. But after 45 years of profiting from special treatment, luxury developers and rich homeowners now have plenty of cash to lobby for the maintenance of their prized subsidy.

Note: we explain how we calculated the property-tax takes here