Yes. But not just London. I'm 300 miles away in the Lake District and can't access mail in any form either. The site Downdetector says there have been issues since midnight, but as usual BT status page doesn't admit there's a problem (at least not here in cumbria where it says all is fine!).
It's not just a BT problem though. There appears to be some kind of major DNS issue affecting all sorts of sites, such as AOL, Tumblr, the Huffington Post, Yahoo! amongst many all over the world. So not BT's fault, I just wish they'd keep us better informed.
And it's unreachable in Surrey too.
Service status page on BT . com says
" Thu 05/09/2019 at 07:33
BT Yahoo customers unable to access their email account
Estimated time to resolve: Ongoing
Were really sorry but weve got a problem whereby BT Yahoo customers are unable to log into their BT mail accounts.
We're trying to fix the problem as quickly as we can."
also in Eastbourne status phone number at least says they have problem 0800 1690199
Cannot access email. Even via webserver.
Cannot see any information anywhere.
If you check the BT Status page you will find that there is an ongoing problem