In the early 1900:s many car companies including Rolls-Royce only supplied the chassis and coachbuilders did the rest.
From 1939 the coachbuilder Park Ward had been a wholly owned subsidiary of Rolls-Royce. It wasn’t until early 1946 that Rolls-Royce provided their own bodywork. When they introduced their Bentley standard steel saloon, it used components made by Pressed Steel Limited of Coventry in place of a coachbuilder's hand-formed shapes.
Useful external links
The Coachbuilders Encyclopedia, an amazing site about coachbuilders, old and current.
20-Ghost Club, a club for owners of all pre-1940 Rolls-Royce motor cars.
Barker & Co, London, UK
Barker & Co was founded in 1710 and was reformed as Barker & Company (Coachbuilders) in 1905. After the 1920s they seemed unable to keep up with the use of light alloys for framing. In 1938 the company fell into receivership and its brand name and business were taken over by its long-term rival Hooper & Co.
Apart from Barker supplying bodywork for Rolls-Royce, they also supplied coachwork for chassis made by Bentley, Cadillac, Daimler, Duesenberg, Mercedes-Benz, Napier, and Packard.