Tax disclosure details between Switzerland, Germany and the UK could mean up to SFr47 billion (around $51.5 billion) could leave accounts in the Alpine state, squeezing its economy, according to consultancy Booz & Co.

In the UK-Swiss agreement, signed in September, holders of offshore accounts in Switzerland will pay a one-off charge of between 19 and 34 per cent of funds to settle old tax bills. Swiss banks will pay the UK an up-front sum of SFr500 million. The agreement takes effect in 2013, subject to legislative scrutiny in the UK and ratification by Switzerland. Negotiations on the issue started in October last year.

From 2013, a new withholding tax of 48 per cent on investment income and 27 per cent on gains applying to those who have not previously disclosed these assets will ensure the effective future taxation of UK residents with funds in Swiss bank accounts. The new charges will not apply if the taxpayer authorises a full disclosure of their affairs to HMRC.

The German deal with the Swiss authorities follows broadly similar lines to the UK one.

However, a European Commission challenge this week to the UK and German tax deals means they are far from certain. The EU’s tax commissioner, Algirdas Semeta, says the agreements cut too far into the EU’s remit over such issues.

The outflows due to the UK and German clients pulling out their money in the wake of the deals constitute about 2.3 per cent of the total offshore assets held in Switzerland, Booz & Co said.

That outflow will reduce revenues for the Swiss wealth management sector by more than SFr1 billion, Booz said.

The crackdown on Switzerland’s centuries-old tradition of bank secrecy is seen by industry figures as compressing the country’s bank margins, because managing secret bank accounts in the past was a low-maintenance job, while providing more “value-added” service such as investment advice requires more staff and cost. (To see a recent article on the issue, click here).