This morning at 00:18 BST the cable connection went down. Service was restored at 01:00 BST.
It wasn’t just the cable modem that went – all of the TV channels turned to snow, and this was backed up by the SB4100 diagnostics page, which showed 0 for the signal level. No, I’ve no idea who tripped over the data cable, but like a good admin I went to bed and waited for someone else to call in the problem 🙂