After a few days of trial and error I have now succeeded in using Thunderbird to access my primary plusnet email account.
Prior to the migration I had two plusnet email accounts in the format
husband@username.plus.com
wife@username.plus.com
I accessed my husband email account via three routes:
Thunderbird 140.6.0esr (32-bit) under Windows 10, imap
iPhone 7, imap
Outlook Express under Windows XP, pop3
The mail is set to clear off the server after a month, so only the pop3 account contains a full email history.
After migration iPhone and Outlook express still worked fine (except for duplication of pre migration emails in Outlook Express). However Thunderbird would not login to the server.
I did manage to login to Greenby, but had to use email address in the format
username@username.plus.com
I discovered my wife's email did work ok with Thunderbird after migration still using wife@username.plus.com
So I changed my Thunderbird server setting to
User Name : username@username.plus.com (had been husband@username.plus.com)
Port: 143
Connection security : None
Authentication method: Password, transmitted insecurely
No changes made to Outgoing Server settings
THUNDERBIRD NOW WORKS.
I would welcome suggestions on alternative, more secure, options for Connection security and Authentication method
