Agency and temporary workers: overarching contracts of employment - zero hours contract
A zero hour contract generally is a contract where the employer does not guarantee to provide the worker with work and will only pay the worker for those hours which are actually worked.
Whilst a zero hour contract does not include a minimum hours work guarantee, it may contain examples of other obligations on the part of the employer - for example, it may contain a provision to pay a retainer.
You should not conclude that a contract cannot be an overarching contract of employment purely on the basis that it is a zero hour contract which does not provide a guaranteed minimum number of hours. You should fully establish what, if any, mutual obligations exist in the contractual arrangements.