Is it a young plant? Is it in an exposed position? We have had such a long cold winter, something that camelias don't like.

Linda again.
I live in Glasgow a lot further north than you in Essex. I have checked my camelia, but it is looking good. I often find living in the city is just that little bit warmer.

it could be Iron Deficiency, you would need to feed a liquid feed as this works immediately and the plant can reach the nutrients quickly. Use a sequestrian feed, then maybe pelleted acid food as this feed your plant for up to 6 weeks.