At around 00:40 we saw a number of BT circuits drop and reconnect. From the pattern of the lines which dropped, it looks like something within the BT network broke and re-routed traffic. We'll be in contact with BT for more information regarding this.
Lines had reconnected by 00:45
BT have confirmed that this drop was caused by them performing emergency planned work - however they also said that they failed to let us, and other ISPs know about this work. They are investigating why they didn't inform us, and we have also asked them why they didn't seamlessly move traffic of the link before their work.