I've just received this email (supposedly) from HMRC, addressed to the first part of my email address:
HM Revenue & Customs
You may be able to get a tax rebate of £268.25 from the last year annual calculation of your fiscal activity.
As part of the new procedure of tax returns, you need to create a Government Gateway account. Requests for tax refunds are time limited and it is vital you cоmplete your claim as sоon as pоssible.
The Government Gateway is the UK's centralised registration service for e-Government services. You may enrol for the on-line Services at any time; however, some services need to be activated before you can use them.
Claim now to create Government Gateway account and submit the tax return request.
Followed by a link to click to create a Government Gateway account and view my annual Tax Return Form or to give them access to all my computer information (although they don't mention the last bit).