The Environment Agency's guidance on permits and "general binding rules" for septic tanks and small package sewage treatment plants is now given on the gov.uk website and is comprehensive. In Wales it's Natural Resources Wales.
SEPA (Scottish Environmental Protection Agency) is Scotland's environmental regulator and will help customers comply with environmental regulations. The customer information page should contain all the links to information for private or comercial projects. You can apply online for consent to discharge.
British Water is the trade association for the water industry supply chain. You can view a full list of their - and our -accredited service engineers or view and download their factsheets and publications.