Chris

Your extensions can be moved. To do this, the VM install tech simply removes the extension cable from the master socket, and wires it in to the new VM master socket instead.

Doing this will not in any way damage the BT master socket, which will continue to function as a standalone telephone socket for as long as you subscribe to BT. And if you cancel BT, but return in future, then it will not require a BT tech visit to reactivate.

It is illegal for the VM tech to do anything to the BT master socket that would prevent it from working. If VM do an install and as a result the BT master socket becomes physically unable to receive service from BT in the future without a BT tech visit, then they have done something they should not have done. Accessing the part of the master socket where your extensions are wired in is permitted, and should not result in any damage to the master socket itself.

Within reason, a VM install tech will site your new cable modem wherever you want it. Installing VM means a cable will be run from the street, up your garden and into an external wall box; then cables will be run from the external box through your walls into the house. The cable should be tacked around the outside of the house to the outside of the room where you want your cable modem, and then through the wall to terminate at an internal wall box. Another cable will connect this internal wall box to the cable modem.

If your house is terraced they will not sling the cable over the roof but will have to go through the interior to the room you want, but this is where they may become a little more picky about where they are prepared to install because neatly cabling indoors is more fiddly and takes more time. Be nice to him and give him lots of tea and biscuits.