Thanks, next time it happens I will try Chrome and see what happens.
So it was not logging in again on Safari this morning, just flicking over and over again after putting in user name and password. So after about ten minutes I opened the Chrome browser. It does exactly the same thing with Chrome. The appearance of the page is slightly different in Chrome it is flicking over and over with a BT logo and three moving dots underneath then to the login boxes (which are empty) then flashing back to the BT sign and dots and so on. So now I see, about fifteen minutes later, webmail on Safari has opened, but Chrome is still flicking over.
When it won’t work on safari for me it has always worked on Chrome so yours must be a different problem to mine.