Latest update is that the ECU won't be in the country for at least another 10 days. Apparently it arrives as part of a bulk shipment in a lorry from Germany, then gets unloaded into a depot in Birmingham, then gets shipped to the dealer. When I asked the obvious question about someone putting the part in a bag and Fed Ex'ing it instead, I was told that never happened. I find that hard to believe.
They also told me (again new information they could have given out before) that they cannot swap in an ECU to my car from another one as it has to be married to the car, the dashboard and the keys, so you can't move them around. I am not so sure about that, as you could probably reprogramme it, but at least it's some explanation.
So I called VW UK to speak to Paul Willis, the MD, who I'd written to a week ago and not heard from. I did not get to speak to the man himself, but spoke to someone in customer liaison. She has promised to phone me back tomorrow once she's had a chance to review the case. When I explained the short version, she was very apologetic, something the dealer has never been. I will update this post when I hear more, but unless something happens soon I'm going to reject the car. As ever, I have to do all the chasing. Not all manufacturers are like that!