Can recommend CTC's insurance run by Butterworths. Linked through the CTC site I think.
ALways been very low maintenance on changing details, renewing etc. You get the impression it's a small company with a kind of old school approach.
Works out about 5% of the totals on the bikes in my experience. Not cheap, but cheaper and way for friendly and efficient than say Evans (who quoted me at 15% last time I checked).
I've also heard good things about M&S contents and home insurances for bike cover.