If you are up for a big, unexpected tax refund from the United Kingdom, make sure you know who you are dealing with.

Her Majesty's Revenue and Customs has issued a warning that fraudsters are targeting taxpayers with thousands of scam emails in the run up to the UK’s Self Assessment deadline, at the end of this month.

The scams asks for bank or credit card details so the tax refund can be paid out, and is said to be the most sophisticated and prolific scam so far.

HMRC is investigating and has already shut down networks in Austria, Mexico, the USA, Thailand and Japan.

Revenue and Customs says it won’t ask people for details by phone or email, so if you find yourself targeted, don’t be fooled!