For anyone interested:
The insurer ruled that the driver was at fault on the basis that he reversed into a stationary object that was not directly behind his car.
I was asked to supply two independent quotes and gave details of the original spec of the bike. If I could not supply two quotes I was told that the insurer would ‘assess the cost’ themselves using the internet.
The back end and frame were written off and I have received a cheque minus depreciation for the damages.