Probably plenty of ntlworld customers who haven't changed providers (and are now Virgin Media customers). I think I still had a working email address with them.

This is true. I have seen many working ntlworld.com emails. NTL, when my parents switched from a 56k modem. Good memories. I remember having an argument with my parents about NTL's search engine. They tried saying Google was screwing their computer up because they used NTL search. I may have set Google as their homepage. This may have been deliberate.

My parents still use their ntlworld email addresses. Virgin Media moved all their email infrastructure to Google some time ago, but are now in the process of moving it back in-house.