Found what was wrong with this in the end. Just needed to stop thinking about it too hard!
Set up another user and they were able to get in just fine.
Looked at the differences between the two users, and as I created the account my user was not given a username, and I had given the new user one.
I populated my user name and I also was able to log in.
Fair bit of configuration and tidying up to do, but it all looks doable now.
Hope this helps somebody else.