Apologies for the long post, but it may be useful to someone, so I will try to detail everything here.
OK, so my roof was sticking in the opening process. The roof did not want to leave the top of the windscreen. Boot opened, pump pumped but the roof did not move. Had to use brute force and ignorance to get it open.
I removed the roof lining (two screws either side and three on the leading edge.
I shut the roof with the lining out of the car and it became clear how everything works. Yesterday I was searching forums for suggestions and I came across a roof diagnostic PDF posted on this site by 'seanie' or someone. This was helpful - go read it if you have problems.
I had thought it was the microswitches as this seems to be common but on mine it was not these.
When you first pull the switch back, as the boot is opening, the hooks on the front of the roof release. These are done by cables which seemed very slack to me before they operated.
After forcing the roof open again, I shut it almost all the way so I could see how the hooks met the roof. It was clear that the hooks were not opening enough to clear the catches.
Followed the cables back and sure enough, near the middle of the roof, they can be adjusted. They are a bit like accelerator cables on cars, remove the holding clip, adjust cable and re-insert clip (I broke one of them by using pliers to remove them. I would suggest a small flat screwdriver to ease them off).
Then, bingo, roof opens and closes without issue.
However, if the cables stretch any more, I cannot adjust them further so I am wondering if the cables are available to buy anywhere so I can replace them?
Hope this helps someone.