Ray Smyth:
A Morris artic of North Western Gas Board loading bagged coke for delivery to private houses and business customers.
From memory, I think these Morris lorries had a 6 cylinder petrol engine.
Photo by Stilltime Collection.
Looks like a 4 litre petrol one, although the Saurer diesel was still offered as an option when those first appeared. I seem to recall they were for 22 tons GTW, and sold as ‘Prime Mover’s’ instead of tractor units. 
The next version with the similar Willenhall cab but different front panel still had the option of the 6 pot petrol, the 4 cylinder BMC 3.4 diesel on the lighter models (developed from the Saurer by BMC which is possibly why all future BMC diesels had the fuel pump on the righthand side) and the 5.1 6 pot on the five ton and upwards models. All had the same 4 speed constant mesh gearbox.
Pete.