UK residents with Swiss bank accounts are being warned that they must either provide full details to HMRC or pay over a proportion of the money in their account and a future withholding tax.

The UK/Swiss agreement was signed on 6 October 2011 and comes into force on 1 January 2013. The agreement provides account holders the option to be subject to a one-off payment on 31 May 2013 to clear past unpaid tax liabilities and/or a withholding tax on income and gains for the future from 1 January 2013, or to authorise their bank or paying agents to provide details of their Swiss assets to HMRC.

The withholding rates currently range from 27% on capital gains up to a maximum of 48% for interest or other non-dividend income. Where the payment option is chosen, any past liability to specified taxes will be dealt with by paying a one-off charge of up to 41% of the total value of the account.

HMRC has also published a guide explaining the options available under the agreement, the factsheet provides details of the other ways in which people can ensure that their tax affairs are brought up to date. It includes contact details for those who want to make a direct disclosure to HMRC.

Jennie Granger, HMRC director general, Enforcement and Compliance, said: 'Swiss banks or accountants are writing to people affected by the agreement. Some may be asking customers to close their accounts. If this happens, UK residents must ensure that any outstanding tax liabilities are paid. Anyone in these circumstances is strongly advised to contact HMRC as soon as possible.'