I'll repeat this from the previous thread:
In the UK, get your local phone directory, and look up 'Unwanted Calls' in the information bit at the front. Look for the TPS (Telephone preference service) number. They can stop all double glazing,etc calls. They sent back confirmation of my 'preference' in a week, and these calls then became illegal 1 month after that.
For doorsteppers, I'd suggest you ask them to call back in one hour, since you are currently on the phone to a double glazing salesman. Or stick a NO HAWKERS notice on your front door, and just point to it if they still have the nerve to knock.