tried disabling your anti virus, or it's email scanner. Either could be causing the issues you offer.

Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Thanks very much, will try you suggestions when I get time and let you know the outcome regards joe

What does "refuse to connect" mean? I have 11 or so accounts set up in Thunderbird and the sole btinternet account I have is notable for repeatedly demanding that I re-enter its password.

Like many ISPs, bt provide email and a Web interface to use it in. So long as that works, they appear not to care about alternative channels not working. There are many alternative email providers. Find another one, who takes email seriously. You can probably set it up to re route your existing email via the new provider, so you don't need to abandon the old email address.