Having the same problem with a new Toshiba.
The link above says the box should detect the TV and display a code, but it talks about a V6 box even though I clicked on Tivo first, and my Tivo says to press clear and TV together, wait for two green flashes, enter 0999, then press channel up at 2 sec intervals until the TV turns off, then press OK and should get two green flashes. The first time I press channel up the TV goes off, press OK and get two green flashes, but when I turn the TV back on again the Virgin vol buttons do nothing. I did this successfully for the previous Panasonic TV.
Another set says to press clear and vol up together, then work through the codes given here https://assets.virginmedia.com/help/assets/documents/audio_remote_code_list.pdf
I get two green flashes after trying each of the three codes for Toshiba but still nothing from the Virgin vol buttons.
Any other suggestions?