As I press the clutch there seems to be a clicking noise as the pedal takes up the slack in the cable. From what I can see the white plastic sleeve on the end of the cable moves slightly out of its groove when the pedal is depressed and moves back when released. Any cure or does it need a trip to the dealer and if so, is it urgent?

I'd say a new clutch cable is required

And you were right!
Hope the new cable lasts more than 250 miles

Hopefully replaced with the latest spec cable GVC907059 cable?

Glad it's all sorted.