Hi Gary
I do a lot of builders cleans and use screw fix upvc cleaning products which i highly recommend
The solvent upvc cleaner (product no 93464-81) gets anything off upvc with ease although does stink, they do a detergent kind upvc cleaner (11235-81) which is in a trigger spray bottle and brings upvc up like new mind you it wont get cement of etc like the solvent cleaner does but it will get everyday dirt and grime of with ease.
If i get a exceptionally bad window i use a window friendly scrubber and put solvent cleaner onto that and gently go over the window, then spray on other cleaner a wipe it off with a micro fibre cloth it never fails to work.
Here is s link to screw fix
www.screwfix.comHope this helps a little
John