When I got back, I had the dealer check it out and it was a faulty glow plug control box. This was fixed (partially paid by Warranty Direct - but that is another story ...) and I am happy to report that the car has been excellent since then.
No more smoking under hard acceleration. I have not been able to verify the starting as it was only a problem when it was really, really cold.
All in all - everything is fine now
As I have bought another runabout car, the X5 is now semi - retired and we only use it for family trips and long distance driving. At least it reduces the mileage increase on the car as well as I think it is a lot better for the car to only start - drive for hours, and then stop rather then local town driving.
