An interesting machine.

Unique, in fact in a number of ways, the most obvious being the slat actuated flaps, and the critical trim settings on the tailplane – Penrose wasn’t too happy signing off the type with the latter – rather dangerous – issues, but expansion period numbers were required with immediate effect.

As to speeds, there’s newsreel footage on Pathe and You Tube of the prototype (pre-naming) trumpeting its remarkable speed range.