Laim, see my update above - it's as close as I can get to a legal precedent to answer your question. It is a good point to substantiate what happened - in the eyes of the Revenue, you are liable for all taxes and duties, so you are the importer.
I'm with your Dad. My godfather was the Chief Metropolitan Magistrate of London, and he would say the same thing! He was also a pretty handy amateur boxer so it didn't pay to argue with my Uncle Dai!
My understanding is that the person with the LiPo pack managed to short out the exposed connectors as the LiPo was being taken out of the packet, and once shorted they welded together and the LiPo went up. As the first post says, the LiPo was being rushed to an exit, but was dropped on the mat with the school logo on.
The school claimed on the Club, the Club claimed on their BRCA insurance, the BRCA insurer claimed on the importer, who turned out to be...
The rest of your post above doesn't quite conform to your Dad's, or my Uncle Dai's good advice does it? "Quite likely..." "should be..." "probably..." "I don't know much...". Would it be too much to ask for you to retract that post until you have some form of evidence as to what is required or at least, as in my case, some form of research that might lead us to think there was something concrete there? Just a thought...