Thanks for your replies/thoughts:

Did think soon after my post that what I really needed to do was the tests with the sensor connected, so as to see if the CIS-E is controlling things properly. Therefore at the weekend I simply removed a small piece of plastic insulation from one of the wires (black wire just before the female connector on sensor side) and put the multi-meter's probe point on to the exposed wire (and earthed the other).

Checking how things looked while at idle after taking the car for a 15min spin: The values shown did indeed fluctuate 0.15V - 0.85V as I believe is to be expected from a healthy sensor. Also saw similar if I upped the revs to 1500rpm.

The only annoying thing is that no matter how many times I stopped / restarted / left the car to stand, I couldn't get it to behave badly (hesitations and/or stall). Am therefore going to leave it for a few days then redo the tests as I really want to see what the readings are when the car is misbehaving......

Thanks also for your other suggestions which I have taken on-board and will return to later. Will post any progress.