3 ton open cabbed 6x4 trucks

[David_Hayward (RIP)]

Bill, I believe that you are right. Mr Kelly on his website comments:

A subsidy scheme was set up that encouraged UK vehicle builders to manufacture the design and make it available for civilian users , the idea being that in time of war the civilian owned vehicles would be quickly impressed into military service .

In fact the War Department patented bogie designs and then licensed manufacturers. The War Office had evidently designed [at the Royal Arsenal, Woolwich] and patented five designs of rear bogie:
(i) War department design of four-wheeled bogie for rigid six-wheeled vehicles, Patent No. 264, 548 dated 19 August 1925
(ii) Design of four-wheeled bogie for rigid six-wheeled vehicles, embodying a single spring suspension.
(iii) Design of four-wheeled bogie for rigid six-wheeled vehicles, Patent No. 259, 322, dated 14 July 1925.
(iv) Design of four-wheeled bogie for rigid six-wheeled vehicles, Patent No. 305, 793, dated 15 August 1928.
(v) Design of four-wheeled bogie for rigid six-wheeled vehicles, Patent No. 266, 272, dated 1 December 1925

Hope that's helpful!