You could set a primary password for Thunderbird, forcing a password. Tools>Preferences>privacy&security.

Thanks for taking time to reply to my query I forgot to mention I am using Thunderbird Portable which has slightly different settings for Passwords. I found the location & I have 5 email addresses, it showed all 5 and also showed passwords for each. Now, I only have one password for google for each of the 5 addresses, however Thunderbird shows 5 different passwords, the format is different for each one & they have no common denominator & all are random characters. So, I have no idea what they are for or how they got created & why they are different to my google password!

I did see the option for a master password but this seems to be a one off for getting emails from all accounts at start of retrieval. Not sure this is the way I want to go, so will look into it later.

When I had normal paasword set for server i had to enter password for each email address, this is what I still want to replicate, so still not sure which options to take.

They whole oauth process is about storing an approved access key. Basically you are plain out of luck beyond the master password to encrypt the stored passwords.

See https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password