"Moonlighting" — working a second job on top of your main employment — is increasingly common in the UK as the cost of living rises and remote working blurs the line between work and personal time. It is generally legal, but there are important employment law limits. Get it wrong and you could face disciplinary action, dismissal, or a claim from your employer.

This guide from our UK employment law solicitors explains what moonlighting means, when it is allowed, and how to protect yourself.

What does "moonlighting" mean?

Moonlighting simply means holding a second paid job — whether employed or self-employed — alongside your main role. Typical examples include:

An office worker doing freelance design work in the evenings;
A teacher tutoring privately at weekends;
An NHS employee working shifts for a private clinic;
A full-time employee running an online shop or Etsy store;
A software engineer picking up contract work on the side.

There is no general law in the UK that bans employees from having a second job. The restrictions come from your contract, the Working Time Regulations 1998, and your implied duties to your employer.

Is moonlighting legal in the UK?

Yes — in most cases. But three things can make it unlawful or grounds for dismissal:

1. Your contract of employment

Check for these clauses:

Exclusive service clauses — a duty to devote your whole time and attention to the employer.
Prior consent clauses — requiring you to get written permission before taking outside work.
Non-compete clauses — preventing work for a competitor, or in the same industry, while employed.
Confidentiality clauses — you must not use employer confidential information in your second job.
IP clauses — inventions or code you create during your working hours may belong to your employer.

Breaching one of these can be a repudiatory breach justifying summary dismissal. Even without an express clause, all employees owe an implied duty of fidelity — you must not compete with your employer while employed, use their confidential information, or divert their business opportunities.

2. The Working Time Regulations 1998

Your combined working hours across all jobs are covered. The default weekly limit is 48 hours averaged over 17 weeks. You can opt out in writing, but if you have not, your employer can insist your second job stops taking you over 48 hours.

You are also entitled to:

11 hours' rest between shifts;
24 hours' uninterrupted rest per week (or 48 per fortnight);
A 20-minute break in any shift over six hours.

Moonlighting that eats into these rest periods can create health and safety risk — a legitimate reason for an employer to intervene, especially in safety-critical roles (drivers, healthcare, engineering).

3. Conflicts of interest

Even where the contract is silent, working for a direct competitor, poaching clients, or using employer time and equipment for your side hustle can amount to gross misconduct. The Acas guidance on second jobs encourages open conversations, but the safest course is written consent.

Special situations

Public sector and NHS staff

Many public sector contracts (NHS, civil service, teaching) require declaration of outside interests and prior approval. Failure to declare can be a disciplinary matter regardless of whether the work itself is objectionable.

Zero-hours and part-time workers

Since the Small Business, Enterprise and Employment Act 2015, exclusivity clauses in zero-hours contracts are unenforceable. From 2022, the ban extended to low-income workers earning under the Lower Earnings Limit. If you are on a zero-hours or very low-hours contract, your employer generally cannot stop you working elsewhere.

Directors and senior employees

Company directors owe statutory fiduciary duties under the Companies Act 2006, including a duty to avoid conflicts and not to exploit corporate opportunities. Moonlighting risks are far higher for directors — take advice before starting anything.

Tax and National Insurance

HMRC treats each job separately for PAYE. Your second employer will usually operate a BR tax code (basic rate) on all earnings, so you may owe more or less tax than you expect. If you are self-employed on the side, you must register with HMRC and file a Self Assessment return.

What to do before you start a second job

Read your contract, including any staff handbook incorporated into it.
Ask in writing — a short email to your line manager asking for written consent is cheap protection.
Avoid direct competitors and any use of employer confidential information, contacts or equipment.
Track your hours to stay within the 48-hour weekly cap (unless you have signed an opt-out).
Keep the side hustle out of work time — no evenings-only calls during your day job.
Register with HMRC if you are self-employed on the side.

What if you are disciplined or dismissed for moonlighting?

If your employer discovers a second job and takes action against you, the fairness of any dismissal will depend on:

Whether your contract clearly prohibited it;
Whether there was a genuine conflict of interest, competition, or breach of confidence;
Whether a fair procedure was followed under the Acas Code;
Whether the sanction (warning vs. dismissal) was within the range of reasonable responses.

If you are dismissed and have two years' service, you may have a claim for unfair dismissal. In cases of automatic unfair dismissal (whistleblowing, discrimination, health and safety) no qualifying period applies.

Employers sometimes offer a settlement agreement instead of a formal disciplinary process. We provide same-day independent legal advice on settlement agreements — usually at no cost to you, because the employer contributes to your legal fees.

Speak to an employment law solicitor

Every moonlighting case turns on the contract and the facts. If you are unsure whether a second job is safe, have been threatened with disciplinary action, or have been offered a settlement agreement, contact Deen & Co Solicitors or read more about our employment law services.

This article is general information and not legal advice for your specific situation.

Moonlighting in the UK: Is a Second Job Legal? An Employee's Guide