Following up on baggydaves post, if you don't want your evenings spoilt by unwanted sales phone calls, then go to http://www.tpsonline.org and register yourself. It takes less than five minutes.
It's illegal for a UK based company to make calls to a TPS registered phone, although it takes a bit of time to get onto the database. If you are registered then just saying "registered with TPS" should stop the call immediately. But it doesn't work with foreign call centres, as some time ago I was called several times by somewhere in India (got the number from 1471).
While you are registering for TPS, you can also do MPS (direct mail) and even FPS (fax - if anyone is still using one). And theres even a "MPS Baby" so that your newborn doesnt get overwhelmed with junk mail!