Sounds like its fallen prey to Photinia leaf spot - a wet winter won't have helped. If the plants are still alive, move them to an open, sunny spot, feed with a general purpose fertilizer such as Vitax Q4, repot if necessary - stressed plants succumb more easily to this problem, and it may be that your plants have been in the pots too long, though you don't say how long you've had them. If the plants have a lot of topgrowth, pruning some out to enable better air circulation will also help.