“To govern is to choose”, is what they say, and last year the treasury chose to sue for peace amid worldwide pressure on Switzerland and its banking secrecy. I have to admit, that at the time, it seemed to me to be clear that HMRC and the treasury had chosen a pragmatic if morally difficult deal with Swiss authorities. In effect, Swiss banks would dip into the accounts of British customers and take up to half the balances in a one off hit, to hand to the UK Treasury to make up for previous tax evasion.

The price? An effective amnesty, and the maintenance of Swiss bank secrecy. But, the Treasury put a yield from the deal at £4 – 7bn. That is a significant sum. the problem, is that since that calculation, the numbers have looked a little optimistic.

I have just returned from Switzerland where I did the first interview with new President and finance minister Eveline Widmer-Schlumpf. She was unable to confirm any figure for the much-heralded yet controversial tax deal announced by the Treasury last year. When challenged by Channel 4 News on these numbers, she said that “Britain will get back a lot of money” but it was “up to the banks” and “I can’t speak about billions”. Tax campaigners have calculated just a few hundred million will be raised from the plan because of numerous loopholes.

Read more: Is the UK serious about tackling tax evasion?

It’s not just the proliferation of avoidance schemes that are spreading across the wealth management industry (move the money to singapore/ Panama, or pretend you’re a company, or live abroad). Even before that the Office of Budget Responsibility cast severe doubt on the number in its assessment of the Autumn Statement: “Our initial discussions with HMRC suggest there are significant uncertainties (in particular over the amount of UK funds in Switzerland that would be subject to the deal and the assumed level of compliance) and we currently judge that the yield is likely to be towards the lower end of the range,” it wrote in November (page 118)

So the question about the actual money that will be raised is very real.

02 swissflag 6021 How many billions will Britain get from the great Swiss tax amnesty?

As is a changing international background. For nearly 80 years the Alps have been a haven for the world’s super-rich. Bank secrecy as Swiss as chocolate and pricey watches. But as the West’s tax coffers empty, this famously neutral country is under attack. The Swiss President told me thet “We felt a lot of pressure for years” before explaining that Switzerland was pursuing a “white money strategy”.

But this building symbolises another more aggressive method for pressurising the Swiss: that of the US.  Last week Wegelin, Switzerland’s oldest private bank effectively had to close. Today it was indicted in the US with helping americans avoid tax.  The US is using a large stick and small carrot approach. The large stick is approached to specific legal issues with banks, wheras the small carrot of a deal is dangled in front of the Swiss government. Swiss bankers have been targeted, jailed. Information has then been used on other banks. Eleven Swiss banks are under investigation. Information and names of 4,000 suspected US tax evaders have been gathered. It’s more Jack Bauer to our Jack-anory.

Nick Shaxson, author of Treasure Islands, likens it to an “economic war” that was started by Switzerland, and that there is a “marked contrast” between Britain’s “cosy deal” and the robust approach of the US. He points out that the scalp of Wegelin shows that US authorities are willing to “go to the heart of the Swiss banking system” a bank that had no branches abroad. Wegelin’s boss was one of the main public defenders of Swiss bank secrecy, who justified it on the basis of providing a haven for citizens of “illegitimate states” like France and Germany that spent too much of their peoples’ money.

The UK treasury says it did the best possible deal – but already it is having to talk about changes to prevent the European Commission referring the deal to the European court of justice. If the changes are large enough, it might have to renegotiate the deal with Switzerland. Perhaps America shows that a more hands-on approach yields more tangible results.

Follow Faisal on Twitter: @FaisalIslam