Thanks for the reply, Colin. The sunroof has made a rattling noise since I bought the car, two years ago. Saturday morning, I drove to town (car is always covered by a winter cover and although it was frosty, the sun was warm) there was a loud noise coming from above out heads. I operated the electric mechanism, I know I shouldn't have done this but hindsight is a great thing! Even worse noise and the sunroof is now slightly twisted and won't close. It lift more on one side than the other. I'm guessing I've sheared the gearing?
Not going to attempt anything with the temperatures this low. Stuffed towels in the gap and covered with the waterproof car cover!
I don't have a garage to work in, sadly!
All the best.