Just a follow-up to let you know what I ended up doing.
I did a bit of checking around, well not too much really, but came to the conclusion that trying to go for 3rd party only was looking difficult, so following oxymoron's recommendation of Caravan Guard, I checked with them and found that they could insure the caravan for £157. Now ok, it's a bit unfair since I did indeed take the minimum possible insurance, and I took a large excess. But to put it in context, the Camping and Caravanning Club asked for £293, so quite a saving.
As I mentioned earlier, after what the C&CC club did to me earlier in the year, there was no way that they were going to get any repeat business from me, regardless of the costs.
So, my thanks to Oxymoron.
Peter G. Shaw