The HMRC have issued an excellent guidance document to help you recognise whether the email you have received, which may well state it is from the HMRC, is actually genuine or not.
The content of the guidance includes:-
1. Current list of digital and other contact issued from HMRC
2. How to tell if an email is fraudulent
3. Report HMRC related phishing/bogus emails
To read the document please click HERE
If in doubt, do NOT click on the link.