I have 2 Camellias that haven't done very well either Izzy. I think they like acidic conditions, plenty of water and shade. Yours looks as if it is lacking nitrogen with the yellowing leaves. A good feed would probably help....one for plants that love acidic conditions, Camellias, Azalias and Rhododendrons.

Give them a good Ericacious feed (as Janey says) and a good mulch and water with rain water if poss.

I actually have fed it with a feed specifically for ericacious plants...the one mentioned on here a lot!...but to no avail.I added ericaceous compost as a mulch and also used Sequestrine. Overkill?......or I wonder if something else is attacking it...

The soil around the camellia looks dry, stony and poor. Unless you have put a large amount of ericaceous compost into the planting hole I doubt the camellia is ever going to be really happy. You might find it does better for you in a large pot at least fora few years. The damage to the leaves also makes me wonder if vine weevil aren't eating them.