Hi Phil
Sorry to have been so long replying but have only just got back from holiday. The part that the dealer replaced was, I believe, the 'starter clutch'. It makes sense that this is what could have caused the juddering as although the car is an automatic it must still have a clutch to stop the engine from stalling when you stop and patently it was this same clutch that was not taking up smoothly when starting off. I am glad to be able to report that the judder has now gone and. as another poster mentioned, the car seems much smoother and more responsive now.
On a more general note, Jazz performed well on our long motorway trips to Monmouthshire and gave us a comfortable, relaxed drive with a reported fuel consumption of 48 to 50 mpg for the journeys. Not bad for an automatic! The only discomfort we did feel was when we arrived back home the rather firm suspension showed up just how diabolically badly maintained the Devon roads are compared to other counties we have driven in.
Peter in Devon