I don't know if this is correct but I was told that if you suffer a loss due to somebody else then you have a claim against them for everything in full. But it is normal procedure in this so called civilized world we live in to let your insurance claim of their insurance. But there is nothing to stop you submitting a claim against someone and it is up to that person to be insured to cover his own backside, if his insurance does not cover the claim in full then the person can still be held liable for the rest.

As for your mates claim, he should be able to claim of his neighbour if it was the neighbours car that set alight first, irrespective of how it set alight.

Graham