My Dad had similar thing happen and got screwed over.
While sitting stationary at temporary traffic lights he was hit in the drivers side rear quarter by a Learner on a moped. The moped then proceeded to hit both side doors and the front wing. The moped then accelerated through the red light and off up a side road.
My Dad informed the police but had no witnesses. The police contacted the insured moped driver who admitted they had hit each other but said my Dad had hit him and then driven off!
My Dad was advised that due to no witnesses he should agree joint liability for the accident. He had to claim on the insurance and now his renewal has shot up in price.
Little scroat!
Hmmm ,
a little bit more detail in looking at the damage : position and directionality of scratches in your dad's paintwork , position of any debris from broken indicator lenses ( if any ) on the road beside the car ; position and nature of damage to motorcycle - coupled with other driver's account of what happened - might well have supported your dad's version of events and revealed inconsistencies in other driver's account .
Damage to offside of car / nearside of motorcycle with directionality of scratches from rear of car towards front could only have occurred the way you described or if your dad had happened to reverse into stationary bike and then along it - court would weigh up balance of probabilities , I know which sounds more likely to me .
It comes down , once again , to who is the more credible witness .
Photographs of car at scene , summoning Police to scene ( from which other driver had departed ) will always be helpful .
