As an estimated five million people attempt to file their tax returns online this month, the Revenue has given warning that fraudsters are targeting thousands of taxpayers in a sophisticated e-mail scam.

The scam, known as ‘phishing’, involves criminals sending out thousands of e-mails which appear to come from the Revenue, saying there has been an error in calculating their tax and they are now due a refund.

The scammers then ask for personal bank or credit card details so that the refund can be paid out. In a variation of the scam some fraudsters are phoning people up, posing as tax officials, and asking for personal information so that the ‘rebates’ can be paid.

The Revenue says the fraudsters appear very plausible. The e-mails come from addresses such as refundtax@hmrc.gov.co.uk and claims@hmrc.direct.gov.uk and the website to which they link looks very much like the Revenue’s own website. The sums of money being offered as a ‘refund’ are quite modest and realistic - usually a couple of hundred pounds.

Any individuals who give the fraudsters their details run the risk of their bank accounts being emptied or their credit cards being used to the maximum.

Lesley Strathie, the Revenue chief executive, says: “This is the most sophisticated phishing scam we have encontered. We only ever contact customers who are due a refund by writing to them through the post. We never use e-mails or telephone calls in these circumstances. I would strongly encourage anyone receiving such an e-mail to send it to us for investigation.”

So far the Revenue has received 11.000 reports of scam e-mails though it fears this may be only the tip of the iceberg. It is working with law enforcement agencies here and overseas to close down the fraudsters. It has already succeeded in shutting down scam networks in Austria, Mexico, the USA, Thailand and Japan.

Anyone who receives a suspected scam e-mail is urged to forward it, unopened, to phishing@hmrc.gsi.gov.uk.