The problem with the bank levy and other Pigou taxes

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This is both extremely disappointing and also par for the course:

The Liberal Democrats plan to hit the UK banking industry with an additional £1bn tax bill, which the party says will help eliminate the country’s deficit.

The supplementary charge will be in addition to the existing bank levy, which is on track to raise £8bn in this parliament, said Danny Alexander, the Liberal Democrat chief secretary to the Treasury.

The annual levy on banks, which was introduced in 2010, currently brings in around £2.5bn a year. Mr Alexander’s proposals are expected to take that up to £3.5bn a year.

The point is that the bank levy is a Pigou tax. There's an externality in the market which is not being included in prices. The tax is there to make sure that that externality is included in prices.

The externality is that the "too big to fail" banks receive, as they are too big for the government to allow them to fail, implicit deposit insurance over and above that on offer through the normal regulatory schemes to all deposit taking institutions. This means that they can finance themselves at lower than free market rates and it's the taxpayer that picks up the risk.

The solution, as we noted and praised when the levy was introduced, is to charge an insurance premium on those deposits that are insured in this manner. And that's how it does work: it's only on the deposits of the too big to fail banks, it's only on those deposits which are not insured through other schemes and it takes account of the riskiness of a run in said deposits (thus long term bond finance pays a lower rate than at sight deposits). That's all how it should be.

And the point about Pigou taxes is that it doesn't matter what happens to the revenue. Sure, it's nice to have 'n'all that, but the point is to correct the market, not to raise revenue.

Thus the idea that the rate should be changed in order to increase the revenue raised is nonsense. It's violating the very point and rationale for having the levy in the first place.

It's also entirely par for the course. No politician can see a potential revenue source without wanting to bathe in it. And that, sadly, is the problem with Pigou taxes. They're economically efficient, rational and make the world a better place. Until we come to the politicians who implement them when, over time, they will inevitably lose their original justification and simply become another method of gouging someone or other so as to bribe the electorate.

What's economically efficient, rational and making the world a better place when a Minister's seat is at risk at a looming election, eh?