My book says that by the 1930s Croall bodies were built by HJ Mulliner
Although Croall owned H.J. Mulliner they kept their own name until c.1934.
This Bentley may have been built in the Mulliner works but it appeared on the Croall stand at the Scottish Motor show at Kelvin Hall in 1934.
Perhaps it's possible to find a photo of the car under the Mulliner name?
Here is the illustration with the caption -