Most of the 'better' cars when chassis were the norm, were produced as a rolling chassis, sometimes with a standard bulkhead and radiator cowling, the body builder did the rest. Sometimes wealthy customers would have a body produced to their own specifications. There were Park Ward, Mulliner, Charlesworth, Tickford and Abbot, off the top of my head and a host more which don't spring to mind right now!
Eventually when chassis became unfashionable and structural bodies replaced them, it became impractical to farm the bodywork out because it had become the basis of the vehicle. The larger constructors absorbed some of the skilled workforce from the hitherto suppliers and took the process in-house.
As a matter of interest Donald Campbell's Bentley which is Bluebird blue, is in a museum not far from here, I thought I had photographs of the front of it but alas only the front bumper, which is an earlier style, late 40's I would guess. I am pretty sure it's a very similar front to the picture above.
OK, I just googled 'donald campbell's bentley images' and the one in the museum is about 1936 style, but still a pretty car, also it picked up on his Land Rover, also in Bluebird blue...
