For those of you who actually recall my previous post....
The sunroof was making and odd noise for some time now, in fact for the past two years. When opened, about 2/3 of the way through it would make a loud thud but open normally otherwise. I actually asked Vx to check this when the car was booked-in for service, their technicians 'could not fault it Sir, but we have lubricated it for you'. So I lived with it.
A couple of months ago, the roof wouldn't close. It went forward through 2/3 of the way, but then it stopped and opened again. On closer examination, the wind deflector flap at the front was not folding down, and the mechanism that is supposed to prevent accidental amputations by backing-up when sensing resistance was opening the roof again.
This seems to be a deterioration of the previous condition, i.e. the flap wasn't moving freely and the thud noise was the result of the flap popping-up at once instead of gradually lifting, and eventually is partially seized - it worked if you pushed down the flap by hand, but not when the roof was closing.
Looking at the rails, it seems that Vx applied a generous amount of grease to the actual tracks on both sides of the roof but not to the flap pivoting points at the front which were dry. Applying a spot of my ole' faithful multi-purpose grease directly on the flaps pivots solved the problem - the roof now closes first time, and opens quietly and without the thud!