If I want to discipline someone do I need to have a policy in place to enable me to do so?

Whilst it is not a mandatory requirement for schools to have a disciplinary policy in place, most will of course already have one.   It can be extremely helpful when dealing with disciplinary matters to have a good disciplinary policy which sets out what is expected of the employee and employer in these situations. It is crucial that all disciplinary policies incorporate the provisions of the Acas Code of Practice on Disciplinary and Grievance Procedures as a minimum:

https://www.acas.org.uk/acas-code-of-practice-for-disciplinary-and-grievance-procedures/html

As a side note, neither the Burgundy Book nor the Green Book contain contractual disciplinary procedures. Disciplinary policies and procedures. It is common for academies or multi-academy trusts to seek to introduce their own disciplinary policy after they become an Academy, in place of the existing local authority policy. This may require consultation with the recognised trade unions and care must be taken to establish whether the existing disciplinary procedures are contractual – so legal advice should be taken.

For a compliant school specific disciplinary policy please see:

D20: Disciplinary Policy and Procedure – school

D20(MAT): Disciplinary Policy and Procedure – MAT

D21: Staff code of conduct – school

D21(MAT): Staff code of conduct – MAT