I did a couple of years ago although it was the police who approached me with a NIP claiming I’d hit someones wing mirror and caused a load of damage.
It was a bloody nightmare trying to prove a negative (that I hadn’t done it), but I did get there in the end.
Things to consider are:
1. Reporting the approach to the police – this may backfire though, if they decide the claim is true and opt to charge your dad with a driving offence e.g. careless driving – or whatever the official term is. It becomes difficult because being unable to recollect the incident, can work in the police’s favour.
2. Get an independent damage report done by a local garage. It cost me £50 but stated that there was no damage, or any signs of a repair. It’s a ball ache, but I think this was the thing that finally persuaded plod that I wasn’t to blame.
Good luck
Oh and of course you should ring the insurance company asking to do the inspection independently – it could well be a scam.