In reply to FesteringSore:
Yes, this sounds very much like harassment. I would suggest:
1. Speak to BT on his behalf (they'll need him to confirm you can speak for him) BT will be able to block the number.
2. Write a strongly worded cease and desist letter to the company involved - send it signed for so you have proof of receipt
3. Report the harassment to the police via a non emergency number.
4. Send the details of the company and behaviour to bbc watchdog - they are doing a thing about companies targeting vulnerable people and pressure selling unwanted goods and services
5. Speak to your neighbour about why he needs a tv breakdown contract in the first place and get the other contract cancelled (unless he's adamant that he wants the cover). TVs are cheap as chips if you don't want the latest 56k 4d 300inch screen and as result he's probably paid for a new TV several times over