Just got a phone call from HMRC, which caused me to shit bricks, obviously.
After a minute or so chatting, it transpired that they believe that my previous employer had been paying out to the Student Loans Company via PAYE, in addition to me paying out to them from my own pocket. The upshot of this mistake is that they owe me thirteen and a half thousand pounds, plus interest! The lady I spoke to is going to double check and get back to me tomorrow.
Now that counts as an epic win, from where I'm sitting.
so much win.