I should have kept this one as a puzzle. But as it is captioned on the website I can't really do that.
It is one of a pair which were commissioned by Rover and were built by Crayford. The entire roof and back window is the soft top with no cross members. To do this they added extra strengthing under the floor and up the sides.
However Rover decided not to go any further with the project. The other example still exists and is on the road somewhere.
I need access to my main machine and I will post a rear view of the car later.