Just an update:
Bro took the car for a thrash last night - no light came on. I thrashed it this morning to 4.5k revs, not a sausage - the error seems to have gone ...for the moment anyway!
At the time I experienced limp mode, I was using cruise control. The mech said that it COULD be the case that one of the items (e.g. EGR) might be a bit grubby and just couldn't react quicly enough to the increase in load on the turbo for a second.
In any case, I do expect the light to come back and, when it does, the turbo will be cleaned thoroughly because I have a sneaky suspicion that, although the codes would point to a map/EGR/VNT solenoid - none of these parts is the issue! It seems to be the unanimous finding from a variety of threads on this topic and throughout the forum, that a turbo issue is usually the vanes sticking!!! May as well get down on the vanes before spending money on replacing bits and pieces such as the MAP etc......