Doesn't look well, does it - check the backs of leaves and all stems and branches, including the main stem, particularly at the base. You're looking for possible scale infestation, soft spots in the wood, mouldy areas, weeping areas, anything at all that looks a bit unusual.

If you can't find anything, it may well be a problem at the root, like phytopthera root rot, particularly if the ground where its planted gets waterlogged or doesn't drain freely.

I will check all that thanks.It is planted in gravel with membrane cut out. As it was there before we moved here im not sure what depth of soil there is for the roots. However the soil here is very sandy and free draining. The other thing i was wondering about was possible Magnesium deficiency and treat with Epsom Salts????

I found this website you might find helpful. It outlines ideal growing conditions for Camilias.

http://www.southernliving.com/home-garden/gardens/camellias

The way the green is being lost from the leaves doesn't really indicate a nutrient shortage - you'd expect various discoloration between veins, not from the outside edge of the leaf inwards. I'd also not suspect a viral infection particularly - the yellowing is far too regular for that.

The link is to the RHS page on Camellia and its possible problems, but if you say the soil is free draining, and we had a lot of very dry weather in summer, is it possible it went short of water for quite a while? It doesn't really look as if drought was the problem though, to be honest - you'd expect much more browning and crispiness all over the place with that.

https://www.rhs.org.uk/advice/profile?pid=327