I can recommend the Truecall device which I have had for two years now. Very effective against all sorts of PPI, Injury claims, PC repairs calls. It links to a server in London which allows you to check the calls and the numbers. You can Zap them and they get a very nice message informing them to go away.
Its easy to google to number and see who they are. The ICO website allows you to record these numbers, so that they can take action if there is a number of complaints.

Neil

I should have added, I have no connection with the company just a very satisfied customer.

Last edited by NeilM; 11/03/13 11:58 AM. Reason: Added PS