Why not give these a try


http://www.columbusdirect.com

Have a look at the British Mountaineering Council.

http://www.thebmc.co.uk/membership-benefits?s=6

http://www.thebmc.co.uk/modules/insurance/Policies.aspx

Don't really understand why special insurance is necessary for hill-walking in the U.K as medical care and rescue services are free (at the moment at least). But you could look at Austrian Alpine Club (UK section) where insurance is included in the membership fee.

I'm also a fan of BMC Insurance. You can take out individual membership, or if you're a member of an affiliated local club you can use this service, and that also applies to Scottish clubs affiliated to MCofS.

Their annual policies are terrific value if you're doing a few trips abroad, and the older you get the better value they become......they're about the only folk who don't think people should stop doing anything remotely adventurous as soon as they turn 65!

Thanks to everyone for suggestions both in messages and emails - I appreciate it!