[BigAde]

Thanks Brian. I will check that - plenum drains were cleaned out recently but that's definitely a good call.

However I have an update. I've just had a call from the garage's mechanic saying that they discovered a huge amount of water in the fuel tank. That would make sense as I filled up on the way to work yesterday (yes, definitely with diesel), so I only drove about half a mile on to work after filling up in the morning. With the flash flooding we've been having, I suspect the filling station has had their fuel tanks flooded.

Of course I'll need a new fuel filter and there could be damage to the injectors still.
Not good.
I've spoken to the filling station but they claim to have had no other reports of contaminated fuel.