Criteria for eco-towns were set out in the Eco-towns Prospectus published by the UK government in July 2007 * Eco-towns must be new settlements, separate and distinct from existing towns but well linked to them. They need to be additional to existing plans, with a minimum target of 5,000-10,000 homes * The development as a whole should reach zero carbon standards, and each town should be an exemplar in at least one area of environmental sustainability * Eco-town proposals should provide for a good range of facilities within the town - a secondary school, a medium scale retail centre, good quality business space and leisure facilities * Affordable housing should make up between 30 and 50 per cent of the total through a wide range and distribution of tenures in mixed communitie