You clock off and work another job in the evening. Can your main employer object? There is no general UK rule that an employer can never restrict outside work. Read the contract and consider the facts before treating a warning as a bluff.
In Great Britain, exclusivity terms preventing other work are unenforceable in zero-hours contracts, and protections also cover certain contracts where guaranteed weekly income is at or below the lower earnings limit, subject to the statutory definitions. Dismissal or detriment for breaching a prohibited exclusivity term can give rise to remedies. These protections do not automatically cancel every notification requirement or apply to every part-time worker. Northern Ireland has separate employment law: check the applicable local rules rather than assuming the GB regulations apply.
A contract may contain an outside-work or consent clause. Its meaning and enforceability depend on the terms and circumstances; it is not invariably invalid just because the second job is unrelated, nor does the employer always need to prove direct competition to rely on a valid clause. Genuine concerns can include conflicts of interest, misuse of confidential information or clients, fatigue, performance and compliance with working-time rules. Time across jobs may matter for the 48-hour average limit and rest periods. Employers should be clear about the reason for any restriction, and decisions may be challengeable if applied unfairly or discriminatorily.
Find your outside-employment clause and any conflict-of-interest policy. Check whether your contract is genuinely zero-hours or falls within the low-income exclusivity protections. Ask in writing which clause or concern is relied on, explain how you avoid overlap or conflict, and keep a log of total hours. If threatened with disciplinary action, seek independent advice before resigning, ignoring an instruction, or giving up the work. Constructive dismissal is not an automatic remedy for an unreasonable restriction.
Explore: https://myredundancyrights.co.uk/contact · https://myredundancyrights.co.uk/my-rights
Official sources: GOV.UK zero-hours contracts guidance; Acas 48-hour weekly maximum; LRA employment information (NI). General information, not a contract-specific legal assessment.