PS
Sounds the same doesn't it?
There is a definite legal grounding about paid monies and estoppels which is the route you went down. You do have to prove that you've spent the money and would be financially disadvantaged if you had to pay it back, or if it's outside of 6 years then you don't have to pay it back.
The PSF guys have been spot on where I am and have backed me up with letters up the chain, just waiting for a reply.