I believe that BT also register you with TPS with BT privacy , the telephone preference service, this is supposed to stop marketing calls from UK based tele marketers, but not the international ones
Caller Display is just caller display enabled on your line. You have to pay for this.
if you sign up for Privacy with Caller Display, BT will register you with the Telephone Preference Service. This will completely fail to prevent nuisance telephone calls. In addition, caller display is enabled on your line. Privacy with Caller Display normally has a monthly charge, but if you agree to a 12 month telephone contract, then you can get Privacy with Caller Display free for that 12 months (they actually bill you, but refund the charge on the same bill).
BT will register you with the Telephone Preference Service. This will completely fail to prevent nuisance telephone calls.
That's not true. While there's nothing the TPS or anyone else can do about cowboy calls (usually scams, often from overseas), they are very effective in stopping those from bona fide UK businesses and do take action if the rules are breached.
The best thing the government could do in this area is to prohibit all telephone marketing calls except where the target has positively agreed to accept them. That way, everyone could be sure that any unexpected call was a scam and treat it accordingly; they would then probably peter out.