Here's the walkthrough for installing the TP Link system
https://www.tp-link.com/us/support/faq/1592/
When you get to the existing kit it's referred to as the modem, not the router.
Which means that the front end box needs to be configurable to operate as a modem, and the Virgin router boxes can all be configured to work purely as modems, only when you do configure it as a modem everything else is turned off.
BT used to fit separate modems not all that long ago (I still encounter them often), and that's all the boxes do - perform modem duties.
https://isabela.iweb.co.uk/resize/ZT...qcGcmdz01MDA=/