Hi Chas & everybody...
As far as i know (having dived in Corfu since '87) there is no restrictions on diving in Corfu! The only places i know of with limitations are the Diapontia islands off the north coast... and some deeper WW II wrecks in the Albanian strait!
I would recommend using one of the professional dive centers on the island, they can show you the best dive spots... and you will be a lot safer diving these waters with experienced guides - especially if you want to explore the many caves on the north coast (a must for experienced divers i think!)
This said, i want to emphasize that not all divecenters on the island is what i would call professional! I've had grueling experiences with some dive centers - fortunately no one got hurt... be critical when you talk to the divecenters around the island, try and dive a couple of places and find your favourite...