The Mailing Preference Service (MPS) will prevent the receipt of personally addressed (name and address) unsolicited direct mailings sent from member companies of the Direct Marketing Association, as well as reputable companies which send direct mail.
The MPS is unable to stop unaddressed leaflets. If they are delivered by Royal Mail you can register with their Opt-out service:Door to Door Opt Outs
Royal Mail Customer Services
PO Box 740
Mailings addressed to "The Occupier", "The Homeowner" etc. which include your postal address can only be stopped by contacting the mailers directly asking them to suppress your address details from their listings.