If you are concerned at the level of junk mail you receive through your door that goes straight into the bin (and at the number of trees who lose their lives in the process), then you can opt-out of anonymous mail by contacting Royal Mail, and general junk mail by contacting the Mail Preference Service.
Unaddressed mail
Opt-Outs, Royal Mail, Kingsmead House, Oxpens Road, Oxford, OX1 1RX
Addressed mail
Mail Preference Service (MPS), Freepost 29, LON 20771, London, W1E 0ZT or call 0845 703 4599