I'm a bit miffed Rich, as I gave VM a back up email address at yahoo, 15 years ago, which I had years before joining VM. This was so they could contact me when there were problems, .... and most importantly, verification e-mails to click on.
Simple and free to set up, and I don't know why everyone doesn't have at least 2 mail addresses.
Do that and check that ir sends/receives OK. The new log in is, it seems the only login for VM/O2 now. Then follow the instructions on the new log-in page.
The account e-mail is your 23 year old one, that is in blue link form. click on that. to get the new log-in going.
You'll need pen and paper to note new log in details. A new password could be your old one with a couple of characters added for extra security.
You'll need to enter your mobile number to receive a security code by text.
There will be a four word code to write down also. An e-mail will be sent to your new e-mail address for you to click and confirm.
The choice of log-in can be kept to "password" as I did. (the new one you made up) When finished, Your old VM e-mail will be the same as always, with all your old mails, as it is your account e-mail. And logging on to "My Virginmedia" wil still say, "welcome back Rich" ! So all the same facilities like billing and help are as before.
I found I HAD to link accounts for it to work, ... which it did, first time !
Please note that the above are not necessarily in the order that you will see them.
Good luck