What should I use to clean my chickens’ feeders and drinkers?

You should use a disinfectant which has been approved by DEFRA, for diseases of Poultry including Avian Influenza, such as Nettex Virocur. The DEFRA Approved list is shown here http://disinfectants.defra.gov.uk/DisinfectantsExternal/Default.aspx?Module=ApprovalsList_SI and can be filtered at the top to show those whch apply to AI.