I took out travel insurance with Besso which includes cover for private aircraft rental:
Insurance Services from Besso Insurance Group Limited Besso were efficient and friendly in getting the insurance organised, fortunately I didn't find out what they were like if a claim was necessary. The policy had some optional add-ons (I took out the flying-related ones) and some exclusions. I looked at about 10 insurers who said they covered flying but most of them had lots of exclusions. Traffords and Besso seemed to provide the best cover for flying.
For others looking at this thread re Chandler Air Services, I did some flying with Chandler a few weeks ago and would recommend them. Details are here:
http://www.pprune.org/private-flying...ml#post7672995