In August 24,000 phishing emails were reported to HMRC an increase of 300 per cent compared to the same month last year.
HMRC are currently helping to close down around 100 scam websites each month.
Commenting, Joan Wood, director of HMRC online and digital said: "We only ever contact customers who are due a tax refund in writing by post. We currently don't use telephone calls, emails or external companies in these circumstances. If anyone receives an email claiming to be from HMRC, please send it to before deleting it permanently.
"The increase in reports is partly due to improved awareness of this scam. However, I have no doubt that more of these "phishing" emails are in general circulation than ever before.
"HMRC will do everything possible to ensure those receiving this email know what steps to take to protect their information, and we are working closely with other law enforcement agencies to target the criminals behind this serious crime and see them brought to justice."