The main law concerning Fish and Chip Shops in England is the Food Hygiene (England) Regulations 2006 which originated form EU directives.
The basics of the law are:
Any Food Handling premise has to be registered with their local authority (council).
The law is then enforced by the Environment Health Department of the council through Environmental Health Officers (E.H.O) or Technical Officers who visit premises in order to inspect.
They have the right of entry, at any reasonable time, day or night. They often carry out routine inspections where they will arrange an appointment in advance, but they can also just turn up, typically where they believe there may be an issue. This may be where there has been some cases of food poisoning which they believe you may have caused, or because they have had a complaint from a member of the public. If they find companies in breach of Hygiene Laws they may; order the company to make some improvements (Hygiene Improvement Notice). They can also close premises (Emergency Prohibition Hygiene Notice) if they think there is an imminent risk to public health, or start prosecution procedures that can result in heavy fines and even prison sentences.