Clive,
I do agree the world of insurance is a very murky place, mind you it isn't dissimilar to many of the other 'burdens' us poor clients have to bear. The usual motto 'caveat emptor' is always worth bearing in mind.
However, the point of the message was that I do feel that towbars are relevant when considering insurance. After all if one is wrongly fitted then the whole structure of the vehicle can be put at risk, not to mention the possibility of disaster with the trailer, which usually then ends up on top of the tow vehicle. So I have no qualms about either disclosing this fact, or paying any excess for it. I have no inside knowledge but it wouldn't suprise me that the CC's insurers are already factoring this into their quotes, even tho' they don't specifically mention it. They would be kinda daft not to seeing towing is kinda their business.
Have a good one.