This is a topic for suggesting sentences to instantly quench a cold-call salesperson who is claiming to be doing a "survey".
{surveys are permitted even if your phone is listed on the Telephone Preferences Service for not receiving sales calls}
Don't be upset at the thought of lying to them since they are almost certainly lying to you!
OK here's one for starters.
"Sorry I can't talk to you because I'm in the bath and the telephone might electrocute me!"