Let's sum up the coachbuilders rejected for this 1929 Bentley Speed Six -
Thrupp & Maberly
Corsica
Gurney Nutting
Mulliner
Barker
Windovers
Park Ward
Freestone & Webb
T.H. Gill
Brainsby
Martin Walter
James Young
Carlton Carriage
Thomas Harrington
Motor Bodies
William Arnold
Harold Radford
George England
Vanden Plas
Hall Lewis
Arthur Mulliner
Charles Clark
John Charles
Alford Alter
Thomas Hayes
Lucius Green
So let's try to narrow it down even more -
The coachbuilder's name is xxxxxx xxxxx (six letters and five letters)