Hopefully this will make some sense. I've tried to show this as simply as possible.
The window failing to go up could be caused by the cable pulling out of the green plastic runner due to the plastic breaking.
It is possible to remove the plastic part from the runner and twist it round so you can see the back side of it. You should be able to see which part of it the cable pulls through as the plastic will be broken or mangled. That is the area we want to fix.
Cut out a small square hole from the green plastic part. There will be a 'blob' of metal crimped on to the winder cable, so when you cut the hole in the plastic, it needs to be either above or below the 'blob' depending on what side is broken.
We then cut a small piece of metal and put a notch in one end. The notch must be big enough for the cable to go through, but small enough so the 'blob' on the cable wont pull through it.
Push the piece of metal through the green plastic so the notch goes round the cable. This piece of metal will now stop the 'blob' on the cable from pulling through the plastic.
NOTES:
The hole in the plastic must be sized so the metal fits tight in the hole.
The metal piece cannot be too big so it doesn't catch/foul any moving parts and must sit flush on the side it was pushed in.
Ensure the metal 'blob' on the cable is positioned correctly in the plastic before you push the metal piece in.
The metal piece pushes in to the plastic from the 'flat' side as shown in the picture. When the window is screwed back on to the green plastic runner, it will stop the metal plastic piece from working itself out.
If the re are any questions, please ask - I'll try and help where I can.
If this still isn't clear enough, and someone can give me a green plastic part and the cable, I will do this again and then post up pictures of the actual fix.
Thanks to IanG for the web links.