Your chances are quite good Andy. You need photos and something to show the size of the hole - measuring tape, CD etc just something to show scale.

Phone the roads department and get a claim form. Send off the photos and a copy of any work invoice, receipt or quote. Send it recorded delivery.

They may say "get lost" and its here that you keep at it. Eventually you will get it. Some local authorities are better than others though.

Edit: oops just saw its been filled-in Might still be worth a try though. They will have a record of the date the hole was filled in and your receipt will be dated. You've nothing to lose.

Edit2: £550??? For ONE wheel and tyre? Made of gold is it?