For about 10 years I have used btinternet/btopenworld email addresses from when I used to have a dial-up account with BT (haven't had BT as my ISP since!). Later they changed their Ts & Cs so you either dialled up every 90 days to preserve the email accounts; or pay £1.50 x 12 months for a 'premium' email service. Needless to say, I just dialled up 4 times a year.
The latest announcement about the dial-up ceasing does not cover this, although their webpage on this
http://bt.custhelp.com/app/answers/detail/a_id/44702... does say "Your email service won't be affected by this change".
That is, so it seems, true! I called BT (0800 917 9987 - helpful Belfast call centre) and they confirmed that if you have existing basic, free BT email addresses then all you have to do is access email accounts within every 150 days (she actually said via via webmail)
even if you are not with BT as an ISP and you don't subscribe to 'premium' email either. As per this
http://bt.custhelp.com/app/answers/detail/a_id/43867...
The switch to Critical Path from Yahoo is a separate issue but they say that Outlook etc configurations will be unchanged.
I'm getting a personal stand-alone domain for email in any case now, but thought that the stuff about retaining BT email addresses without cost may be useful to others in a similar situation.