Another update............. I have replaced the battery and it is now turning over much more crisply (the old one's indicator was black, which according to the technobabble meant it was poorly). After fitting the new battery, the next (very cold) morning I started it immediately after the glowplug warning light went out (which is what I've always done) and it still spluttered and chugged a bit, accompanied a bit later by lots of smoke. I shut it down straight away, then left it for 10 minutes whereby I turned the key again and waited a good 20 seconds after the glowplug lamp went off and it started perfectly. I was always of the opinion that these beasts could be started as soon as the glowplug lamp went off, but maybe I've been doing it wrong for the last 3 years, although saying that it has been getting bad over the last 6 months, so maybe the battery was kyboshed after all. In addition I've given it some diesel injector treatment and that seems to have improved things more. I thought about dirty glowplug relay contacts - I know it doesn't take much in the way of contact burn to reduce the current delivered and since the car is over 3 years old this could be a possibility. Any more ideas would be greatly received.