HMRC is gearing up to send out a second tranche of letters later this month to taxpayers it believes may face tax liabilities under the UK-Swiss Tax Cooperation Agreement, and is warning that anyone who fails to reply can expect an investigation into their tax affairs.

CIOT has been sent a sample of HMRC's letter, which will be issued only to the individual concerned and not copied to their adviser or agent.

The letter's opening paragraph gives the recipient a date by which they must respond, and says that if they do not do so, HMRC 'may start a detailed investigation into your tax affairs ' and that 'in some cases this could be a criminal investigation'.

The letter, which is sent by HMRC's specialist investigations offshore coordination unit, sets out three options. Recipients can complete certificate A if they have no outstanding UK tax liabilities; certificate B if they are already registered for the Liechtenstein disclosure facility (LDF); or certificate C if they do have outstanding liabilities but are not using LDF.

Individuals are advised to 'consider their position carefully' before making any submission, as making a false disclosure or completing a false certification could result in prosecution.

The letter concludes by stating: 'It maybe that you have not told us about any income or gains because of an oversight on your part. However, if you do not reply to this letter, we will take it to mean you have made a conscious decision not to tell us.'

In evidence to the Public Accounts Committee (PAC) in October 2013, HMRC admitted its forecasts of how much would be raised as a result of the UK/Swiss agreement were 'inaccurate' and it was likely to see only a quarter of the original forecast of £3.2bn.

HMRC officials told MPs that the total recovered so far was £782m, saying that the 'secrecy' surrounding the Swiss banking system was to blame for the shortfall.