Have turned off the radiators off in the rooms we don't use, the conservatory, spare bedrooms etc, and they are now freezing if I go in there.
Is there any chance of a burst pipe if the room is so cold? Have got the sitting room really toasty.
Rather than turn the radiator off completely, turn it off and then open it by about 1/4 turn of the tap. That way you keep a tiny flow circulating and it won't cost you much money.
If you have controls with numbers on them (thermostatic control valves) then they usually have a setting just below "1" which is the frost setting (looks like a snowflake)
If only a rotary valve, then it's just guesswork. Maybe leave the valve open s half a turn or so.
Either do as above, or if you want to turn them off completely,dose the system with antifreeze(use approved type).This will stop the heating pipes freezing, but not any others in the locations mentioned.