I didn't know about the IOM accident mate, sorry to hear about your bike
As Dave suggested is the only way to get them to pay you what you think it's worth.
When i wrote my limited edition Mini off a few years back now, they first offered me £1100....I paid £1650 for it & knew it was still worth that. All i did was photo copy magazines etc to show its worth & eventually they paid me £1650.
Then again they had to really, as i had already been notified by the DVLA that somebody had tried to re-register it...so they'd obviously already sold it!
Good luck mate....you going to get another NSR?
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88 NSR250 R2J (work in progress!) & 05 Aprilia SL1000 Falco