Virgin media dont need phorm to track what is being downloaded on their network. the operative word is computer their network. As we are all connected to Virgins Network to get our internet all they require are tools to they already possess to track network use by reading the logs/packet sniffers. These sort of tools give you bandwidth used, what sort of traffic is being used ip source ip destination etc etc.
Example :-
http://lachniet.com/cheaplogging/