Click on the check service status at the top right-hand side of the page, as there might be a reported fault in your area
If you sign-in to https://my.virginmedia.com/home/index#. You can run the broadband test, it might determine a fault
somewhere.
Else
We'll need more information to form an opinion
What package do you have with VirginMedia?
What home device/s are you using for YouTube?
Is it with Wi-Fi or with a cable connected to the Hub?
Have you run speed tests @ https://www.speedtest.net/ ?
Have you set up a BQM (Broadband Quality Monitor) @ https://www.thinkbroadband.com/ ?