Those are aphids, and if you use something to get rid of them, the ants will go away.

Not sure they're aphids, I think they're scale insects that just haven't laid their eggs yet. Spray with Provado ultimate bugkiller, making sure you get the underside of the leaves covered with spray in particular. The ants are neither here nor there, its the honeydew produced by both aphids and scale they like.

Thank you both for your suggestions..I have never had this problem on any of my plants or shrubs,before ..Is it particular to Camellias,or a general thing?

Camellia is susceptible to scale infestation, but so are many other plants. Infestation rates vary year on year.

Ok,thanks..I will spray tonight,when it's cooler,and the sun has gone off it.much appreciated..

I'd go with black fly [a colour form of aphid/greenfly] and they are being farmed by the ants. The blackfly secrete a sugary waste [honeydew] and the ants use it as a sugar source.

Thanks Sbg,whatever they are,they are horrible..I don't normally use chemical sprays,but I found some lurking in the shed..so had a go with that last night,and just looked this morning,and it appears to be working,as some of the leaves don't look as infested.. ..It's very difficult spraying undersides of leaves, for it not to come back at you, so I had my version of a Jihab over my nose and mouth. an old tea towel :o)