The illegality should not be limited to a violation of prior license conditions but can also consist, for example, of a violation of other administrative rules or general principles of environmental law such as BATNEEC
(Best Available Technology Not Entailing Excessive Costs) or ALARA (As Low As Reasonably Achievable).
A Guidance note on iron, steel and nonferrous foundry processes lists the control requirements to meet the BATNEEC
(Best Available Technology Not Entailing Excessive Cost) principles.
More recently the criterion to be adopted has become BATNEEC
('best available technique not entailing excessive cost').