Just to see if I got it right:
Great Britain
8-cylinder
#1: available also as a 6-cyl
#2: not a very minor marque like Vulcan
#3: closer to Hillman than others
#4: more significant brand...
Alvis
Arrol-Aster
Arrol-Johnston
Belsize
Beverly-Barnes
Hall
Hampton
Hillman
Lanchester
Owen
Railton
Rolls-Royce
Sizaire-Berwich
Sunbeam
Vulcan
Wolseley
It can't be a Batten, Brough-Superior, Duplex, Leidart, Palladium, for #2 and 4
It can't be a Burney...seems to young for being a Daimler, Ford, Jensen, Riley, Talbot or Triumph...
Leyland?