Camellias are hardy in the UK (apart from a few specialist ones). I'd suggest that you harden it off, as with any plant that is going from inside to outside. Put it out in a sheltered spot (up against the house?) each day, but bring it back in around dark. Do this for a couple of weeks, then leave it out overnight. After a couple more weeks it will be ready to plant out (or keep in a larger pot if you are on alkaline soil). Water with rainwater as they don't like the lime in tapwater.

Agree with Volunteer - but at least we know why the leaves and buds are dropping - it's cos its indoors and you're not watering it enough - they don't really respond well to drought situations, so water it well and keep it watered, but not standing in water. If its really dry, give it a good soak by standing it in a tray and watering - what it hasn't absorbed after an hour, discard and then allow it to drain down. If you want to keep it in a pot, use ericaceous compost, they prefer acid soil. If you plant it out (assuming your soil isn't chalk based, which means its alkaline) don't plant it in an unshaded east facing position - early morning sun in winter on frosted buds means the flower buds will fall off.