Sorry for the delay posting this, and thanks for all the MSO texts.
Last night a firewall config change was made on the BE side of our link to them. I am not sure we had a planned works notice. Anyway, the effect was to drop all sessions to us, and at least one other ISP. They reversed the change just under 20 minutes later and lines reconnected.
We are in discussions now as to what they were doing and why?