Hi guys and thanks for the replies. it has been the roadbike for the last couple of days so I haven't managed to have a look at the Mtb since you've posted but rest assured I will.

Alan it does happen in different front gears though it has to be said that the bike spends 95% of it's time on the large gear at the front.

The problem at the rear is across all the range and as the bike is roughly 15 months old most things are in pretty good shape.

A thought has just occured to me.(not something that happens often)

As I spend most of my time in the large gear at the front and that includes whilst climbing could that be putting stress on the chain and hence stretching it, because if that's the case maybe I be better off going to the Lbs and letting them sort it out.

Once again thanks for the replies.