Unfortunately, signing up to the TPS won't completely eliminate all junk calls, since many now originate from call centers outside the U.K. But it's certainly worth it to at least reduce the number of nuisance calls somewhat.
One other tip: You might also receive computerized calls from BT's SMS text messaging service, which allows a text message to be sent to a regular landline number and be converted into speech for delivery. The marketers sometimes use that service to deliver their junk sales pitch as well. You can control the times at which messages can be delivered, or block them completely, by calling 0800 587 5252 and following the prompts to set your preferences. (If your telephone line is set to withhold your number on outgoing calls by default, then you'll need to prefix that with 1470 so that the system can "see" your number.)