What is meant by ‘custom and practice’ in employment terms?

Some terms may be implied through custom and practice in a particular trade or with a particular employer. Terms can also be implied by the conduct of the parties, meaning that they act in such a way that suggests a term has been agreed. 

For example, it may become customary (over a period of time) to leave early on a Friday, or to add an extra day to a Bank Holiday. In order for an entitlement to become established by custom and practice, it must be long-standing, uninterrupted, automatically received, expected and well-known. 

It is not enough to show that something has happened for a particular length of time. Instead, an outside observer, looking at the behaviour of the employees and the employer, must be able to conclude that both parties must have intended their practice to be a contractual right or obligation, with legal force. This is very difficult to establish. 

Sometimes the idea of custom and practice is used to interpret an express term, for example, working out what is meant by 'reasonable overtime'.