Try using the format xxxx.t21@btinternet.com for your user name.
Many thanks for that suggestion, I'm annoyed at myself for not thinking of it! However, fault seems to have been cured as I just tried again a couple of minutes ago and it all works again. It's certainly not a very robust system... 😃
Here is today's 'error of the day...'
Active from 6.30am to 8.20am. I look forward to see what tomorrow brings 🤣
(Tried different browsers, in addition to an android phone- all couldn't connect to ANY BT site!)