The Housing Ombudsman considers complaints using dispute resolution principles and encourages their use by both landlords and tenants so they can resolve complaints at the earliest opportunity. There is a lot of helpful advice on the Housing Ombudsman website.
You can contact the Housing Ombudsman by:
Writing to: Exchange Tower Harbour Exchange Square London E14 9GE
Telephoning : 0300 111 3000 (lines are open Monday to Friday from 9:15 to 17:15)