The States of Guernsey warned islanders on 3rd July that the letter, supposedly sent by the US Embassy on behalf of the IRS, is headed "Final Tax Amnesty Notification" and includes a form that requests name address and banking details, allegedly for use by the IRS to be faxed back to a New York number.

"We have received confirmation from the US Embassy that this letter is a scam designed to obtain bank account details for the commission of identity fraud," the States said in a statement.

"Anyone receiving such a letter is asked to ignore it and to send it to the Data Protection Office or the fraud section of the Guernsey Police," the statement advised.

It has also emerged that residents of the Isle of Man have been targeted as part of the fraud after the Isle of Man Office of Fair Trading, the Office of the Data Protection Supervisor and the Financial Crime Unit of the Isle of Man Constabulary all issued a warning about the letters of Thursday.

Similarly, the letters try to frighten the recipients into responding by saying that a tax amnesty currently in place for those with offshore assets will expire next month and at that time not only will tax be payable but that they may be liable to prosecution.

The Office of the Data Protection Supervisor has contacted the IRS at the US Embassy and has received confirmation that the letters did not come from them.

"As with all such scams, the simple advice is to throw the letter in the bin. On no account should anyone provide personal or financial details unless they are completely satisfied that the request is legitimate," the Manx government stated.

"If any one has responded to one of these letters, they should as a matter of urgency inform their bankers. If anyone loses money as a result of responding to the letter they should contact their local police immediately," it added.