Indeed, I have the same problem (spinning cog).
I think it is caused when you log in and tick the "stay logged in" (or whatever its called) box. The cookie that is set from doing that is what is causing this issue.
One good workaround which has not been mentioned yet is to launch an incognito window in your browser. This will not present you with a spinning cog and you can access your mail fine. You will also not have to clear your cookies on normal browsing for the time being- although you might have to eventually when they fix it.
The better option is not to use webmail in the first place and use the proper tool for the job, a mail client.
"The better option is not to use webmail in the first place and use the proper tool for the job, a mail client."
That suggestion is not connected in anyway to the current problem and does nothing to help solve the issue with the webmail. A bit like me taking my car to a garage because of a fault, only to have the guy in the garage tell me i should ride a push bike because it's better for me.
Can now log in using forum suggestions - logged into my BT Account through google link, then to Email & it connected fast & fine.
On the other thread by VBrantuo 'BTinternet.com Email not working or recognised!! Help' CLgg30340 replied with a link which worked perfectly - thank you