Hi Allan,
It is primarilly a Bridging crane used by Royal Engineers. We knew them as the Mk.5, the earlier one had similar cab and running gear as Militant Mk1 but with beams instead of springs on rear bogie. The Mk5 engine is much bigger than the earlier one, being the AV760, of 215 bhp against the old 11.3 litre, 150 bhp Militant. When working in REME workshops, I spent some time repairing and testing cranes, these and the earlier Militant, also the rather dated RAF ones which still used the Matador engine but with a later cab.
They lift a max. of 7 tons on wheels and 10 tons on blocked......that is over the rear at shortest radius.
Going by the census number on yours, "EY", I would think it is an early one as a lot were in the "FU" range. All up weight was 26 tons.
Richard