In reply to Train to Summit:
I've used BMC insurance and made claims with no problem at all.
I've also used some Swiss insurance (the name escapes me) that was very cheap and specifically for helicopter rescue in Switzerland. Not tested as I didn't claim.
Sometimes I just travel with my First Directory annual travel insurance policy and a level of self insurance. They've always paid out really easily and promptly whether medical, delay, damage etc.
The proof of the pudding is definitely not the cheapness of the cover but whether it pays up and helps out promptly when you need it