They can't do this, and it certainly wasn't anything to do with the loss (unless your fine was for Arson!).
Do NOT get no win no fee because this is a simple case and they can't order you to pay this. Quote the FSA and their rule on repudiation of claims. If you need more ammo let me know and I will come back on tomorrow to advise. Just rushing out the door.
Don't panic. If you are being candid on here and this is the only reason, you will be fine ! You don't even need legal aid. They will take that letter back ;)