The scammers are using the end of the tax year as an opportunity to send out bogus emails in the hope that the timing makes you more susceptible to them and more likely to take them seriously.
It seems that there a lot of emails purproting to be from HMRC with various messages about tax refunds, late returns or coding updates which are not from HMRC at all.
HMRC will not send unsolicited emails of this type and it is likely that they are from villains intent on obtaining your bank details and personal information with a view to relieving you of some of your hard-earned cash.
If you do receive one of these, if you check very carefully the address that it has come from it may show you that it is not HMRC. Also, if there are any links in them, you could hover your mouse over the link and you should see where it would take you - probably not HMRC! Don't click on the links as you may get an unpleasant surprise in the form of malware.
Another thing to avoid is opening up an attachment as these may contain viruses which could infect your computer.
If in doubt find a legitimate phone number for HMRC and contact them but do not rely on the authenticity of a phone number or email address shown in the email as these could be bogus. Make sure of the number is from a reliable source so you know that you will be talking to the real HMRC not somebody pretending to be.