Interesting, thanks. This morning I taped up the air intake hose (which can't have been the problem originally as it has only been flapping about since the dealer mended the last pack failure) as the ED cars don't let much air into the engine bay.
It then ran on 5 cylinders with the warning light yellow from a mile in to the journey until about 2 miles in - when it cleared and was fine for the remainder of the 6 hours or so driving I did today. Can't have been too hot then...
I wonder if using Super might help - though everyone except Sainsbury's (who's fuel is actually BP) charge crazy money for the stuff these days. I also wonder just how long Super sits in the tanks and whether it is actually higher octane at all! V Power I get, it is the most different of all the Super fuels in composition, but the rest I'm not sure about, and I have not so far noticed any difference in the drive or economy when using Super for a few tanks.