Well - I take it all back!
Took the car in on friday to BW Mascot.
The mechanic "Dave" listened to my description of the problem, took the car for a test drive, looked at the Rosstech error log I had brought with me and agreed with the diagnosis. They had the new ignition switch in stock and everything was sorted in a day. I have driven the car for a couple of days now and the problem is definitely fixed now. They did a neat job too, no damage to the steering column covers.