Taxpayers have been warned about an internet scam trying to exploit those who think they may be eligible for a rebate.
The email, claiming to be from HM Revenue and Customs, advises people they are in line for a £300 windfall and invites them to provide personal details.
HMRC has announced that it will be contacting six million taxpayers over the coming months in connection with overpaid PAYE tax bills. One million people are also due to be told they have underpaid their tax bill for 2010-11 and face demands of up to £600 each.
A spokeswoman for HMRC said anyone who receives the email should send it to firstname.lastname@example.org before deleting it permanently. "We only ever contact customers who are due a tax refund in writing by post," she said.
The adjustments are part of an attempt to clear a £2.5bn backlog dating back to 2003. A new IT system has made it easier to spot over and under payments.