Interesting Dominic.
Does the Egr valve have a sensor/wiring as well as the actuator? (Eg 5 wires rather than 2)

Several cars that just have the actuator use the Inlet air flow to monitor the Egr performance as obviously Egr flow bypasses the inlet air flow sensor. So if Egr is open when it should be closed then the Maf would read lower than expected. I suppose this should show an Egr code rather than a Maf code but how would the system differentiate between the two?