I do not know the full extent of the cause, but reading both the NATS release and the Eurocontrol CFMU release, the problem looks to be that the plasma touchscreen telephone system is not configuring correctly so new positions cannot be opened to split the sectors. There is no possible redundancy/back up system for a system failure of this kind.
Una, London area control do not telephone the next sector to coordinate, it is all done electronically and the telephones used for amendments or to pass other details. The only exception to this is that not every other centre/airfield are connected to the electronic coordination system.