We struggled to get insurance on ours. It was also empty while we had work done. We had to use a broker and paid £700 and that was with a lot of exclusions. Now we're living in it we insure through NFU who seem very good.
We insure through www.larkinsurance.co.uk they do a specific policy for listed properties and the policy is really comprehensive with lots of options you can add on for expensive contents or stuff in the outbuildings etc.