Not only is that bike a Panther, it's a 1939 model, as indicated by the tank badge. 1938 was a panther head decal. More impressive than that, this is a Model 100 (600cc) De Luxe.
Modern folklore would have us believe that a "De Luxe" Panther was a contradiction in terms, because it was significantly more expensive than the basic M100, and anyone who could afford that should have bought something else.
Main feature of the De Luxe was the twin headlights. This was a Phelon and Moore patented system. The headlight pivots are at top and bottom of the shell, but are away from vertical. Electrical supply to the right headlight is via an open copper contact between the two shells. A proper left hand twist grip operates the left shell. Twist the grip, the left shell turn to the left, sending the beam left and down into the gutter, simultaneously opening the copper contact and extinguishing the right shell. Voila, dipped beam! Other De Luxe features were the dash, with space for an optional 8 day clock, rubber mounted handlebars and a twin bezel Miller tail light that apes the headlights.
The high level exhausts were a further option, so (presuming it's Stuart's outfit) Stuart is a pretty keen and dedicated sidecariste. Snappy dresser, too.
JFerg