The story I got from the seller is that he bought it off a friend who had stored it for ten years with the intention of making a castrol race rep as he owned a bodyshop.
He then bought it and stored it again before deciding to get rid a year later.
I checked the MOT's and it did no mileage at all during his ownership (not sure why he would MOT it though).
The story seems to check out as the engine and internals were covered in mould. A quick disassembly and clean up has brought it up to new looking. It certainly doesn't look like anything has been touched in a very long time.
I am waiting for log book to turn up, this may provide further answers...