Back when I was young, the eighties, there were some well documented cases on TV Documentaries and in the newspapers of insurance companies failing to pay out and refusing claims on seemingly trivial grounds.
One documentary about how the insurance industry works showed them failing to pay out on a Ford Orion that had been fitted with XR3i Cloverleaf Alloys and a rear spoiler which were deemed a modification and thereby made the insurance void. The car was a total loss after it had collided with a tree - was a bit suspicious as the owner was reckoned to have been drunk driving, hit the tree, walked home and reported the car stolen in the morning to avoid a drink drive ban. Insurance company suspected this but couldn't prove it so returned the annual premium to the owner and told him that because of the mods, he was on his own.
Another simpler case was a chap who fitted a new stereo to his MK2 Escort and claimed on the insurance when the car was genuinely stolen. Car was recovered, burnt out, with the stereo missing. Owner admitted that he'd upgraded the stereo and the insurance company refused to pay out on the grounds that "He had made the vehicle more desirable to steal and hadn't notified them of the increased risk" - I kid you not!
Many Insurance companies are at best lying, cheating weasels and will do ANYTHING to get out of paying if there is any chance that they can find a way. The two examples were from the eighties when the insurance first went mad, going from 9 to 20 groups. It has become much, much worse since then and even if you have a perfectly reasonable, honest claim it can still take ages to resolve. My last one was 6 months and the insurance company did me out of £300 (out of pocket expenses) when my car was written off when parked quite legally it was struck by another car.
Insurance companies can bite - read the small print.