I’ve had a look today and the collar was pressed well on the half-shaft, but I discovered plenty of rust, mud and general crud between the axle end face and the back of the brake back plate. This crud was preventing the surfaces from mating cleanly together, thus allowing the extra end float. The surfaces were all cleaned off and coated in waxoyl. Once everything was reassembled the extra end float disappeared and I was just left with a very small amount end float which I think is acceptable.
With the devalutaion of the pound you may be better getting your seals/bearings etc from lighthouse mate,