Hi, I think this may be caused by some sort of bug, if you turn the leaf over you should be able to see it on the leaves and it needs to be treated. I think it could be needing a feed but if you go onto the gardeners world site you should be able to find more info on there, hope this helps

Check the stems for scale insect, plus have a look for aphid infestation. Scale and aphid produce sticky honeydew, to which pollution sticks and makes the leaves black, sometimes also causing sooty mould to develop. Spray the plant with Provado or a scale/aphid treatment, avoiding spraying the flowers if possible. Now would be a good time to give an ericaceous feed - use something like Azalea and Rhododendron feed (not just sequestered iron).

Thanks Fran44 & Bamboo. Your comments are very helpful. I have sprayed my camelia already and today it is looking a lot better. I shall feed it later on Apologies if you have already received this reply, but I suddenly thought that although I had written it I didn't submit, so here goes. Happy Easter