[MovedGoalPosts]

You are pushing the connection well beyond what is intended. Indeed if the splitter in the loft was not something created by ntl installers, you've probably contributed to your own poor signals.

The cable from the street should only be connected direct to cable boxes. One split might be introduced to allow service of two subscribed STBs, but the signal levels would need to be checked by the installer.

If you have a third split to send a signal to an TV only without the use of a STB, you need to remove that. Instead if one of your STBs has an analogue passthrough, feed the output from that to the third TV. However be aware passthrooghs are no longer supplied by Virgin Media so you should be looking at alternative ways of gettinig terrestrial signals bakc to your house, i.e. a roof top aerial.