On 15/03/18 15:30, David wrote:

I assume that he wasn't interested because a conservatory is usually
exempt and you weren't modifying the drainage (which usually requires BC
approval) but just building over it.

That was the gist of it. In fact the drains were new a few years before,
but already inspected and passed.

I was surprised he wasn't interested in the building over - but he said
that effectively, the conservatory didn't exist with regard to any
jurisdiction he had, so...