Official figures released by HMRC suggest that it will only receive a fraction of anticipated revenues from the one-off Swiss Capital Tax levied as a result of the landmark UK-Swiss tax agreement which came into force at the beginning of this year.

Initial government projections suggested the Treasury would benefit by £5bn over the next six years from the deal which Chancellor George Osborne called 'the largest tax evasion settlement in British history'. The £3.2bn of revenues expected this financial year have already been included in the government's borrowing figures.

However, this month's HMRC statistics on tax receipts show that so far it has received a total of just £747m as a result of the Swiss agreement. This is made up of a £342m pre-payment in January this year representing a 500m Swiss franc guarantee made by the Swiss Bankers Association (SBA), followed by payments of £258m in July and £147m in August.

Ronnie Ludwig, partner in the private wealth group at Saffery Champness, says inflows are now expected to continue taper off rapidly, since deductions should have already been made by now.

Ludwig said: 'Although the figure of £3.2bn may have been in the right ballpark in terms of what the HMRC is owed, it was massively optimistic to expect that they might actually recover this much.'

Under the terms of the agreement, accounts held by individual UK taxpayers that had not been declared to HMRC previously were subject to a one-off levy of between 21% and 41% to settle past tax liabilities on 31 May 2013, as long as the account was open on 31 December 2010 and on 31 May 2013.

From 1 January 2013, income and gains arising on investments held by individual UK taxpayers in Swiss banks are subject to withholding tax of 40% on dividends, 48% on interest and other income and 27% on capital gains annually. If a taxpayer opts to disclose their accounts to HMRC and settles any unpaid tax due, then the withholding taxes do not apply.

The terms of the deal mean the SBA can only begin recovering the money it paid out in January once 800m francs (£556m) has been paid to the UK authorities. The association said many British clients are likely to have opted for voluntary disclosure while others hold resident non-domiciled status, both factors which would reduce the amount handed over.

In a statement, the SBA said: 'The possibility can therefore not be ruled out that either none or only a small part of the bank's guarantee payment of 500m francs will be recovered.'

Ludwig said: ' A large number of Swiss bank accounts with connections to the UK are not actually held by individuals, but are bound into complex webs of offshore subsidiaries and trusts, whose beneficial owners are not recorded anywhere. It is extremely time-consuming and expensive for HMRC to investigate offshore structures. When the taxman gets a sniff, assets can be switched from one jurisdiction to another at a moment's notice. Nothing is going to change until we have internationally agreed standards, under which accounts and assets are recorded together with the names of their beneficial owners.'

Separately, HMRC's statistics also show that revenues from Stamp Duty Land Tax are growing rapidly as the property market heats up, with the monthly take up by 25% in July compared to the same month last year, and August's figure also jumping by 15%. Saffery Champness calculates these are by some distance the highest monthly figures since the height of the last boom.