In reply to duchessofmalfi:
Yeah, phoned the BMC and although they used to be a bit more flexible apparently the US has been completely ripping insurance companies recently so they now will not cover trips there longer than 45 days.
The BMC recommended Snowcard, Dog Tag and Sports Insurance Direct or something (who I think are behind Protectivity). Protectivity say they won't cover climbing without an instructor etc (!)
Currently having an interesting chat with someone at Dog Tag about what big walling is, and Snowcard only cover up to 60 days. Grrrrr.
Had a look at AAC (presume you mean American alpine club) looks like you can't purchase insurance if you are a UK resident, though perhaps you could get membership giving you $10,000 rescue cover. However, good old Austrian Alpine club may still be best, giving you a bit more cover at 25,000 euros. the medical cover is not great, but I guess that's where your additional travel insurance kicks in.
Any further ideas still welcome