Update:
Passed the MOT this morning.
The tester gave it an advisory because of slight oil misting round the top of the shock absorber. That will be the PlusGas I squirted to free the gland nut so that I could check it was really tight.
I'll degrease the shock absorber and then see if it is really leaking.
No comment on the play, which has virtually vanished with time and warmer weather.