I've just had an engine warning light diagnosed on our 40,000 mile unmodified TDV8 as a failed EGR valve by our local dealer. It took them 2 hours, but that's another story.

Unfortunately the part is on back-order at the factory so we'll be waiting a while...

Has anybody else had a similar experience and got any advice to pass on?

Not sure if my problem is the same as yours, but I have engine fault appearing along with a loss of power. If I rev it to over 2000rpm, I can eventually get the engine management to take over. I can at least drive normally for a while!
One Dealer investigated, albeit not too deeply, said it might be fuel pump. I would have thought that if it was the fuel pump, it would happen all the time.
One other dealer didn't want to know!
When I can find one who knows what they can do about it I'll let you know!
At the moment, I don't use the car very much and I put up with it when I do.
Will have to solved soon, as I will crossing Europe with it in October!
UPDATE!!
Went to dealer today and he said it was the particulate filter. Not quite sure what was up with it, as my French is limited!! My message centre hasn't requested that I empty the filter for some months. Car ran smoothly there and back. Time will tell on this one