ah Jonathan, I thought I was alone
I have Fedora Core on another partition but I couldn't run it for a few days to test as some of the software I use isn't available on Linux (they won't even consider a port). Besides, I seem to remeber when I signed up to ntl the person on the phone saying, "It is a Windows PC Sir isn't it?"
The DHCP renewal (I'm starting to think) might be a coincidence as the last time this happened I was sitting at the machine 11am with expiration of the next day.