There is no clear definition of what is a Crown Body.

The enabling statute of an organisation will often state whether or not a particular organisation should be treated as acting on behalf of the Crown. For instance, the Radiological Protection Act 1970 provides that, with certain exceptions, that the Protection Board created by the Act "shall not be taken to be a servant or agent of the Crown of the enjoy and status or immunity of the Crown", and the National Health Service and Community Care Act 1990 states that "no health service body shall be regarded as the servant or agent of the Crown or as enjoying any status, immunity or privilege of the Crown".

In contrast, however, the Building Societies Act 1986 states that the Building Societies Commission performs it functions "on behalf of the Crown." The general trend is for enabling statutes to state that the new organisation is not a crown body.

In relation to other public bodies - where the legislation does not clarify whether or not the organisation is or is not an agent of the Crown - a recent Home Office document states that:

"The question of whether an organisation can claim crown immunity depends upon the degree of control which the Crown through its ministers, can exercise over in in the performance of its duties. The fact that a Minister of the Crown appoints the members of such a body, is entitled to require them to give him information and is entitled to give them direction of a general nature does not make the corporation his agent. The inference that a corporation acts on behalf of the Crown will be more readily drawn where its functions are not commercial but are connected with matters, such as the defence of the realm, which are essentially the province of Government." (Consultation on Reform to the law of manslaughter, 2000)

There is no doubt that Government Departments are Crown bodies. Local Authorities are not crown bodies. The prison service - since it is also a department within the Home Office - is also a crown body. Police forces are however not crown bodies.