In reply to a post by adslmax:

Never touch BT cable from the A & B terminals - it illegal to do it.

Nothing worse than the police knocking on you're door after a friendly neighbour grasses on you for touching the A & B terminals

Worst still: opening up a BT66B external junction box by the front door!

I disconnected the bell wire behind the master socket, few years later got a new master socket fitted by bt while investigating a dropped leg on our connection guy doing the swap never mentioned it, so how much to they really care?