Er, 1 ... 300TDI.
It's behaving like a petrol engine missfiring on one cylinder. Had it on the last Disco and it was the IP playing up. On this one I've changed the IP, all the injectors, cleaned the sedimenter and changed the filter, still no luck.
I'll check the tappets, but I doubt that's the problem. Now thinking about buying a J, Jeee, Jee, Jeeeee ... American car because I've heard they are so relyable!