If you start with https://www.britishairways.com, it should work (some other auto-saved URLs returned an error 404 for me but removing everything after "britishairways.com" got it working). I can log in and see my flights etc. as per normal.

However, MMB returns an error, "We're sorry, but ba.com is very busy at the moment, and couldn't deal with your request. Please do try again - if it still doesn't work, it may be better to try again at another time."