Thanks for the replies so far.
As some have said a standard travel policy may be okay, and that's the bit I'm struggling with. For my own peace of mind I want a policy that, should I need to use it, I know will be okay. My impression of most insurance companies is that if they can find a get out clause at claim time they'll happily use it.
Of the policies I've looked at that covering cycling the provided catogories are usually touring or racing, with nothing which would fit Audax. The closest I've found so far is this one:
https://www.sportscoverdirect.com/sports-travel-insurance/The 72 hour limit makes it a none starter
On a general note I'm also happy to pay more to be with a reliable company as opposed to one that provides a cheap quote & you only find out how they keep their costs down when you need their help (1)
(1) When I was dinghy sailing, most people used one company whose premiums were relatively high, but they covered all your dinghy kit, including extra masts and sails, replaced old for new, and always settled claims promptly and efficiently. We were all happy to pay the higher premiums knowing that it was good value for money.