By dialling these numbers you may reduce the number of silent calls but they are not a foolproof way as predictive dialling software is used by other companies as well as telesales firms.

Only 40 telemarketing firms have signed up to the Silent Callgard service that means they will not call your number.

Telephone Preference Service: (to prevent direct marketing calls) 0845 07 007 07

Silent Callgard Service: 0870 444 3969