Hi Plymouth_Cleaning
Have you checked out the Scrim City site they do PVC Cleaner?
http://www.scrimcity.co.uk/catalog/advanced_search_result.php?keywords=PVC+CleanerThere is two sorts one solvent which might move it.
For my Cleaning I use Ammonia, thats not bad.
There was a bit on earlyer posts and they said to use CIFF Powder (is it?)or any of the bathroom cleaners you know the stuff like Jiff it should come of with one of those if not cheak out the titan range. I have been using the oilflow 141 and the MDR they are both good for staining. http://www.titanlabs.net/info.htm#cs22
Dont think Mike stocks but can be purchased from the windowclean centre 0800 413512 or scrimcity.
When using always test first not sure what all results will bring
Hope this helps
Alan