hi Graham,
Your Dummy Axle was made by Royal Ordnance Factory, Nottingham. Going back to your first message, I do not think it was intended to tow the full Antar and trailer, although there were times when Scammell EKA 's towed full trains in order to clear obstructions. In the SEME Recovery Data, it lists recovery of a fully laden Antar and semi trailer as N/A, a tractor on its own would require a front lift of 5.5 tons, rear lift being 8 tons 8 cwt, which could be reduced by 1 ton, which may indicate removing rear wheels (?). Using a dummy axle for a Antar plus trailer, would not impose any weight on to the driving wheels of the towing vehicle, so lack of traction could occur. My only experience of this Dummmy Axle was load testing them when working in REME workshops.
Richard