Ziggy, I think you could end up spending more to fix this bike to original standard than it would be worth. I have repaired a written off HP4 Carbon a few years ago, it was pretty much cosmetic damage and cost more to get right than I got for it but was a great experience for me.
Sometimes an insurance company will allow a vehicle to be auctioned off with a strict caveat that it cannot ever be put back on the road. Looking at this bike there are a few pointers that this is one.
The ignition key is not an original one for the HP4 and the state of the chain leands itself to the fact it has sat in a breakers yard for months whilst insurance etc. is settled. Don't forget it's been down the road a few times by the look of it too.
There are checks you can do from the VIN if the seller will provide it, also if you can track down the supplying dealer I'm sure they will be happy to confirm service history and possible why it is track use only.
I'm positive this bike will go for more than the ?5200 it's sitting at just now as it is ideal for a track rider.
I have decades of experience in repairing insurance written off cars as my Dad was in the trade for years and have owned dozens of great cars that were bargains due to this. Tread carefully Ziggy and remember if it looks too good to be true then it is.
JimmyMac