In all the furore around the Budget, the Spending Review and so on, many have ignored the introduction of the Lib Dems so-called "mansion tax for tax-dodgers". This "tax", which only affects properties worth over £2m, was actually the closing of a loophole.
The loophole in question - which allowed people to avoid stamp duty on expensive properties using offshore companies - was theoretically sealed from the start of April. A super-duty of 15 per cent was imposed on the purchase of properties worth more than £2m by companies; and an annual charge of up to £140,000 every year was levied on them once they were bought.
Well, in theory, at least. Like almost everything else the Lib Dems have promised to do, this has all fallen down around their ears. Why? Well, that's all down to clever tax lawyers seeing a new loophole, accidentally provided by short-term lettings website Air BnB.
You see, there's an exemption written into the rules, which lets off properties which are "open to the public" from the new tax. It's meant to exempt stately homes and museums, which are often private homes but open for viewing over the summer, and quite legitimately put the earnings from the tea room into a company. No one wanted them to be hit with a levy intended to stop tax-dodging oligarchs.
Of course, when you close a loophole intended for oligarchs, you'd better be sure not to open another, or their lawyers will spot it. One bright tax lawyer came up with the idea that if you offer to let out your property - regardless of whether you actually let out - it's technically "open to the public", in that literally anyone could pay to go and stay there. Provided, of course, they can afford whatever you are charging.
It's probably pretty reasonable to charge a fortune for your One Hyde Park flat, given the amenities, which include all your mail being X-rayed, iris recognition in the lifts, panic rooms, bomb-proof windows, a 21-metre swimming pool, a cinema, a golf simulator, a wine cellar and room service via a secret tunnel from the five-star Mandarin Oriental hotel next door.
So, you advertise your One Hyde Park flat (registered to an offshore company, of course - as 59 out of 77 flats in the building are) on Air BnB, no one volunteers to pay the huge fee you ask for, and you save yourself 140 grand in tax. Worst case scenario, you have to let out your flat to someone, but you probably don't care, because you can arrange to be skiing in Gstaad for that week anyway.
Some of the properties currently being offered on AirBnb are at eye-wateringly high prices. While there is no evidence that, for example, this £3,175 a night flat is using the loophole I've described - I can confirm from a tax lawyer for a major firm (who asked not to be named) - that offering your flat out to rent has become the standard advice being doled out to his firm's "high net worth clients".
So, Air BnB will doing brisk - perfectly legal - business as every oligarch and his babushka registers. And no one who is well advised will pay the Mansion Tax-lite. And the Lib Dem plan is yet another failure. Thanks internet!
Of course, while there is some schadenfreude to be had from yet another Lib Dem flagship policy running aground on the rocks of reality, it's also a salutary lesson for policy makers on the sheer difficulty of clamping down on tax avoidance. Even if they close the "AirBnB loophole", the lawyers of the rich will find another, as long as the "open to the public" exemption still exists.
This story is a great example of how the government's attempts to clamp down on tax avoidance amount to a ridiculous game of whack-a-mole - if we want to get serious about tackling tax avoidance, what we need is root and branch reform, not tinkering at the edges. Put away the mallet, George, and pick up a bazooka.