R v Northumbria Police Authority [1989] QB 26

The home office decided to keep supplies of CS gas and extra batons in a central store that a Chief police officer couldn’t obtain in an emergency unless his police authority gave him permission. If the police authority denied permission then he could use a special procedure to get them.

The police federation challenged this, saying that the relevant Police Act conferred no such powers.

However the residual prerogative power of the crown to keep the peace, unamended by legislation, remained.

There is no need for a statute to state what the prerogative is: it is a common law right. This prerogative would be meaningless if it could only be used in an emergency and this measure is designed in order to keep the peace.

Since the Police Act had not wholly supplanted the prerogative, the parts upon which the Act didn’t touch remained.