If you get called an awful lot, this might be an idea...
... if you've the time to set it up. Buy a premium rate phone number and set the rate to £5/min:
ezinearticles.com/?Buying-A-Premium-Rate-Number-All-You-Wanted-To-Know&id=511923
and every time someone tries to sell crap to you, say you're interested, but could they call back on the other line?
( Colonel Boris "...a desperate Buzzfeed imitation...", Fri 4 Sep 2009, 10:05, 5 replies)

You can't set the rate to £5 per minute
The maximum retail rate on a UK phone call is either £1.50 per minute (p0) or £1.50 per call (ff21), including VAT.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Fri 4 Sep 2009, 10:09, closed)

Also
If you want to be a premium rate service provider, you need to comply with certain terms of service as per PhonePayPlus (previously ICSTIS).

(Not the greatest hoop you'd ever have to jump through, given the plethora of pre-recorded tarot/psychic reading lines that exist at present)
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Fri 4 Sep 2009, 10:12, closed)

Damn you and your laws!
£1.50 a minute ain't bad, still, if you can keep them talking...
( Colonel Boris "...a desperate Buzzfeed imitation...", Fri 4 Sep 2009, 10:17, closed)

£1.50 per call is better
If you have a "fault" on the line meaning they have to try again when the line drops after 20 seconds.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Fri 4 Sep 2009, 11:02, closed)

Costs...
are £99 for initial setup and 70p per day line rental... you also don't see all of that £1.50, just a percentage.
(SillyMoo, Fri 4 Sep 2009, 11:03, closed)