In reply to balmybaldwin:
It would appear to be a screw-up. I received this from BT's inter-operator notification service at 10:32 this morning:-
"The root cause of failure has been confirmed and is due to a sub-sea cable planned works carried out by a third-party provider. " A subsequent update says they're looking to see if some undamaged fibres are useable.
Post edited at 15:55