Are you at GDS? Please can you tell your friends at HMRC that the login system is the most janky UX I've ever experienced and is prone to social engineering due to how complex it is.
Impossible over the phone as they wanted to send a paper letter to my address and I was just moving to a new place (and doing some travel before that) so I had no more access to the address HMRC had on file.
I finally gave up and just asked my accountant to do it on my behalf. He somehow managed to sort this out with HMRC.
There is no flow to recover your username and password (or generate new one) with your email address which is maddening.
[1] "HMRC rejects Gov.uk Verify", http://www.computerweekly.com/news/450412927/HMRC-rejects-Go... [2] http://www.computerweekly.com/news/450301278/Revealed-The-ba...