Basil plant covered in black/white spots

My partner and I bought two basil plants around three or four months ago. They were doing well, but recently they've begun to look unhealthy. There'd been a small number of white splotches on the leaves, but these have begun to spread over the two plants where before they were only on the Thai basil, and they've nearly covered every leaf. They're not raised splotches, but more indented, as if the colouring has disappeared from within the leaves. These patches are also slightly shiny from certain angles. Within these patches are minuscule black dots. They pattern the areas where the leaf has been discoloured - see the photos for a better idea.

We've tried spraying for leaf hoppers thinking it was them, but the only result that seemed to show was that the plants developed a browning dry look at the edges of the leaves.

Here are the photos:
http://picasaweb.google.co.uk/lh/photo/Py2Oot7-Lvw6NSgwKHoNIQ?feat=directlink
http://picasaweb.google.co.uk/lh/photo/jcZbKqZjaAwRjucQzZIAvg?feat=directlink

Please help!