OK guys, plenty of food for thought, but her is the Audi Specialist's view, for anyone else with this problem.
the MAP sensor which does live in the back pipe from the intercooler does actually read the manifold pressure and sends the signal via the ECU, which controls the wastegate, ie the boost. But what i'm told is that the fault i got is due to either a faulty MAP sensor, giving false readings ot that the wastegate is sticking. if it's the sensor then fair enough £80 or so. and substitution is the only way to really find out. If it's the waste gate sticking then it could be a one off or the start of the end. Seemingly if you can get a hold of a vacuum gage or similar device and check the action, in both directions, of the wastegate, it has to be smooth without any binding or sticking. And you can clean the MAP sensor. So i'll start with the electrical cleaner, and let you guys know how it goes. OK!