On the face of it, the Chancellor played a blinder. His team signing an historic deal squeezing what could be up to £5bn for the exchequer from Switzerland’s infamously secretive bankers for unpaid tax from UK nationals. A handy windfall at a time when the coffers are empty. As George Osborne pronounced tonight: “We will be as tough on the richest who evade tax as on those who cheat on benefits.”

Any Briton with untaxed income in a Swiss bank account right now will face a one off charge of between 19 per cent and 34 per cent on their entire balance to account for past tax avoidance. The Swiss banks will prepay CHF 500m of this in 2013. A new withholding tax from 2013 will remove the incentive to use Swiss banks for tax avoidance purposes. That tax will even apply to non doms.

All well and good? Well it depends. £5bn is clearly larger than the big fat zero that the UK exchequer has earned from these deposits in the past decades. But it is clearly far, far less than might be expected if these tax avoiders were hit in the conventional way.

Crucially the enforcement of this charge will be handled by Swiss authorities. Effectively HMRC has outsourced the collection of this unpaid tax to Switzerland. In return Switzerland basically maintains its sovereign historic banking secrecy.

The tax campaigner Richard Murphy is incandescent about this deal.  He points out that many of these tax avoiders would have been jailed, and believes the payment including fines and interest would be more like 80 per cent rather than 34 per cent.

The deal does seem to be a pragmatic “amnesty” aimed at getting a chunky windfall, at minimal effort to Britain, at the expense of thoroughly (and expensively) enforcing British law. Undoubtedly however, tax haven aficionados, some who have evaded millions, are getting away with more leniency than your average Brit. Rioters facing jail for stealing £3.50 worth of water might feel aggrieved.

But if that thorough application of the law was applied, would we really yield more than £5bn?

Another critique would be that Germany signed a similar deal which has yielded CHF 2 billion of guaranteed payments, four times as much as Britain. Germany’s deal might not get through parliament.

Mr Murphy believes that the German and UK deals have scuppered the chance of an EU wide agreement with Switzerland that would have unpicked Switzerland’s banking secrecy. A classic dilemma of governing. For a significant amount of cash, would you have let Switzerland and tens of thousands of tax avoiders off the hook?

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