I have been sent an email from HMRC saying I have a refund Is this something they do?

No, HMRC never email people about refunds, you may get reminders to do something, but they will never ask you for information or ask you to use a link. It is a scam email and it is important that you do not disclose any personal information. Forward it to phishing@hmrc.gsi.gov.uk and then delete it. HMRC will not reply to you but they will take this seriously and investigate the source.