Hope I'm not speaking (writing) too soon, but further cleaning up and re-checking seems to have done the trick - driven the car a few times now and so far, no lights.
Trouble is, the garage are not sure what finally did the trick.
Tried sychronising on several occasions but gradually became less effective - at first it worked for a short time but lights soon returned.
Anyway, so far, so good - fingers crossed - and thanks all for responding!