So this leads me to believe that actually the insurance companies don't look very hard trying to find a loophole, I think the surveyor came down, spent half a day checking paperwork and seeing that the aeroplane was indeed beyond economic repair and signed on the line rather than a full technical audit.
I would imagine the economics play a big part, if the aircraft is worth £60k they will be loathe to spend £10k on a surveyor going through with a fine tooth comb, who may find nothing wrong. Also, I've seen a friend's policy with a clause along the lines of, if it's a very minor ANO breach and there is absolutely no way it could have anything to do with the accident, then it won't prevent a claim. That said, it would be very unlikely to get off with a big paperwork gap (no medical, no rating, no Cof A) as paying out would surely be seen as supporting an illegal act?