It seems there are two types of EGR- one is located at the front right of the engine, is vacuum operated, and is easy to get at. The other sort is at the middle rear of the engine, and is operated electrically- under the control of a vacuum sensing unit.
The purpose of the EGR is to control exhaust emissions by feeding burnt exhaust gases back into the inlet manifold. If the valve sticks open- the engine is breathing exhaust gas all the time- particularly noticeable at low revs, so this matches my symptoms.
