Thanks Nodge, I was really particular about making sure the injector seats were clean and new copper washers and O rings fitted. Intuatively it all comes back to the injectors and it feels like there's a loss of compression and hence the unburnt...

I have a Diesel Freelander 1 which I use on our smallholding. I had the injector tips cleaned and after refitting there was a loss of power and lots of white smoke on any strain on the engine accompanied by pinking. I think I sussed it insomuch...