Hi Nell51, happy to say I have now resolved this!
It turns out to be quite a fiddly matter of 1) changing your main password (tricky because you need an email address to tell VM to send their verification code to and if you can't get into emails..... it's a dead end! BUT....!) once past this it's fairly plain sailing to 2) setting a new, auto-generated password for the actuall email part of the account.
You get past it by telling VM to send the verification code to a completely different email address e.g. your wife's if it's still working. (it might be that to avoid the email dead end you have to change your main logon email address to the independent one too - I did). Then after clicking 'forgot password' and getting to the verification code page, just copy the code back from your independent email into your VM account's code request window and you should then be able to change your main myvirginmedia account password and re-login using the new password.
Having done that it is necessary to change the email login password which is an auto-generated process....Once logged in to myvirginmedia, click on the Account Settings box; then the Virgin Media Mail Settings box; (then you may need to get another verification code to land on the 'Mailbox App password management' page.Click the red 'generate new app password' button and follow through the steps until you get an auto-generated password in the form of 4 words separated by hyphens (e.g. abcd-efgh-ijkl-mnop). Going back to your main account login landing page, scroll down and clicking on the 'virgin media mail' box should now take you into your online emails B-Boom!
At least, it did for me!
The added complication now is that if you use Outlook on a PC or Mail/other mail client on a mobile then your email accounts on all those things need to have the passwords changed to the auto-generated, 4-word version you got earlier.
Hope that helps! (but if it doesn't, try ringing the help line - they answered withing 2 mins for me this afternoon and eventually got it sorted.)
Steve