This is good advice Whiskas
I registered with the TPS about six months ago when we were regularly getting disturbed by various cold-callers, usually as were were sitting down to our evening meal >
I can't remember the last time I was disturbed by an unwanted sales call.
I have also registered with their Fax Preference Service (for work) and Mail Preference Service (for home) which is available from the same site. It can reduce the unwanted junk faxes and mail received.
They also run an Email Preference Service, but I think it's only aimed at legitimate email marketers. I don't think it'll actually reduce spam