Brilliant, thanks! I'd looked on Amazon loads of times too and never found it!There's one here at amazon.co.uk: Good Pet Stuff HL4 Hidden Litter Pan
Shipping is really high, though, since it ships from the USA.
There's another one here, with free shipping worldwide: http://www.fishpond.co.uk/Pets/Good-Pet-Stuff-HL4-Hidden-Litter-Pan/0643500929794