It can be a bit of a guessing game in most countries, but the UK make it very clear for you.
If the controller tells you to "Contact xxx on xxx.xxx" then your details have been passed on already and they are expecting you. If they tell you to "Freecall xxx on xxx.xxx" then your details have not been passed on and they are not expecting you, so you have to give your full details over the radio.
I wish other countries adopted the same system
dp