Guys,
Just completed my annual Data Protection course, I have to do these as part of industry regulation and in the most part they are a PITA, but sometimes this crap comes in useful.
It reminded me of this ->
http://www.tpsonline.org.uk/tps/index.html
It's the telephone preference service, if you register your telephone number with them then any unwanted calls (unless it's from a company you already deal with) should be stopped. It's an offence under OFCOM rules for a company to call you if you are registered (although no-one has ever been taken to task,, yet). I used it on my home land line and it does stop all but the companies who flout the law by using off-shore dialers (shows up as 'International' on your phone when they call)
It might be useful for you, or not, you choose.