Using the old NTL TV boxes, It was possable to do this
Internet > TVBox > Computer
This is because one of the old NTLTV Boxes had a built in modem, it was for engineers use only, but it was possable to use it, but it required messig around with the router and tv settings, then you could skip the need for a seperate modem, But when Virgin Media took over, they removed all the redundent hardware from the boxes

, I got told off by NTL on one occasion for using the engineers testing port to connect, and not the separate modem they sent me.
Nowadays an external modem is virtually always required, Especially for Broadband.
Everyone Be Cool, You, Be Cool.