No they didn't specify why they didn't specialise in my sort of boat. It was built in 1981 so the 30 year limit shouldn't apply. I assume it is either because it doesn't fit within one of their accepted manufacturers, or it is the single handed element.
Their on-line quote system allows you to select from their database of boats, unfortunately the Achilles 840 isn't in there.

Nickrj: I expect that that will be my policy, I will just try not to get damaged until I get back to the Brest to Elbe sea area