In webmail:
- sign into the ntlworld.com account
- select ⚙ > E-Mail > Auto forward …
- select enable button, enter virginmedia.com email address into address field
- select Keep copy of the message if you wish to retain a copy; otherwise it is permanently deleted after forward
- select Apply changes
FYI auto-forward will only forward those emails that arrive in your ntlworld.com email account's Inbox folder. If an incoming message is incorrectly identified as spam it will not be forwarded.
FWIW if you use webmail to read your emails then consider adding the ntlword.com email account to your virginmedia.com account by signing into latter and selecting Add email account , as highlighted below:

--
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click
Mark as Helpful Answer and solved, or use
Kudos to say thanks