Tally, not sure if it's available to you in the UK, but many people here use Micro-mesh attached to a magnet cleaner to remove coralline in acrylic tanks.
https://www.micro-surface.com/defaul...at_Disp lay=A
It is similar to sandpaper, and available in differing grit sizes. Use the finest ones for polishing out fine scratches or for removing coralline. There is a kit made with this stuff as an acrylic scratch remover as well.
http://www.sisweb.com/micromesh/craf...s.htm#aquarium