I took the car to the Vauxhall bodyshop this morning. They took photographs and made notes of the corrosion on the sunroof frame plus a couple of bubbles that are forming at the bottom of the drivers door and a small amount of rust that is just visible under the plastic surround for the rear screen wiper arm. They said that they would contact Vauxhall and let me know the outcome, so now I just have to wait. The rust bubbles are just as bad as the ones on my old 2.0 GLS estate which was 6 years old and just out of warranty when I bought it. It would appear that the later cars are slightly worse than the older ones for corrosion despite the zinc coating etc. Still I must say that it certainly drives much better and smoother than the older model plus it has more toys to play with so it's not all bad news after all! Will let you know what happens next.