Thanks very much Solair and Coljack for the info.
I connected it back up, as I think it must be a ring, and now for some reason its fine - all the sockets are working, and it hasn't tripped back down again.
Also thanks for the advice about the radiators. The one I've already installed is...
Hope someone can help me with this as I don't know very much about circuitry :
Does every house/apartment have a cable running somewhere from the last socket on the circuit - from a socket near an outer corner, and is it essential to keep this connected?
A fault developed in the bedroom...