For the market survey calls, about one a day, I have been using the "Im sorry, Mr Jenks has passed on" response for some time. It is usually effective and gets a polite "sorry to have taken your time" reply.
But for the next "Windows" call I will try telling them I no longer have a computer since "Wiltshire Police" took it away. I think that might be interesting.
Mostly I don't really object to these people, imagine what it is like to be paid to work in an Indian call centre having to make these calls. So I am never rude or offensive.