[Gpa113]

Thanks both for your help.

 Before purchasing anything specific,  I thought I'd try what was around the house.....

1. Warm water and washing up liquid. 
Let it soak for 20 minutes, then tried to clean the marks off.   Looked great  until I dried it, and it wasn't really any better at all! 

2.   Cif, or Jif, or whatever its called this week....
Applied a tiny amount onto a  Jay cloth,  and just worked it around. Rinsed, checked, and repeated. 
After 15 minutes,  and getting braver each time with more Cif, it worked a treat.

Now very nearly back to how it was before I mucked it up.  Will refit, using a  very small amount of canopy glue, and hope it bloody works!