Entering address does indeed show the sensible result that ties in with what my ADSL reality used to be: Between 10.0Mb and 19.5Mb (Estimated speed: 17.0Mb).
Also gives sensible figure for my neighbour based on his telephone line.
As I said at the start, I'm not too concerned, just intrigued by the inconsistency.
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.