Running a Side Hustle While Employed: What Your Contract Can Restrict

Introduction: The Contract You Signed vs.

The Business You Want to Start

In the current economic climate, supplementing a primary salary with a secondary income stream has shifted from a hobbyist's pursuit to a financial necessity for many UK workers.

However, the romanticised vision of "being your own boss" often collides with the cold, hard reality of the employment contract you signed.

That document is not merely a formality; it is a legally binding set of shackles that can restrict your ability to earn outside of your nine-to-five.

Before you register a company, buy stock, or print business cards, you must conduct a forensic examination of your employment terms.

Failure to do so can result in disciplinary action, summary dismissal, and even legal action for damages if your side hustle is deemed to harm your employer's interests.

This guide bypasses the generic encouragement found in most business advice.

Instead, it focuses on the mechanics of UK employment law, tax thresholds, and the specific clauses that dictate what you can and cannot do while employed.

We will look at the trade-offs between sole trader status and limited companies, the reality of the £1,000 trading allowance, and the specific risks posed by conflicts of interest.

If you are serious about running a side hustle without jeopardising your main livelihood, you need to understand where the red lines are drawn.

The Big Three: Restrictive Covenants in Your Contract

Most employees assume that as long as they do not work on their side hustle during office hours, they are safe.

This is a dangerous misconception.

UK employment contracts often contain "restrictive covenants" that extend their reach beyond the workplace and outside of working hours.

There are three primary clauses you must locate and scrutinise in your contract: the Exclusivity Clause, the Non-Compete Clause, and the Conflict of Interest clause.

1.

Exclusivity Clauses

An exclusivity clause explicitly prohibits you from working for another employer or running your own business.

Historically, these were strictly enforced.

However, the law has shifted in favour of the employee for lower earners.

Under the Exclusivity Terms in Fixed Term Contracts Regulations 2022 and amendments to the Employment Rights Act 1996, exclusivity clauses are unenforceable if your guaranteed weekly income is at or below the Lower Earnings Limit (LEL) for National Insurance contributions.

As of the 2024/2025 tax year, the LEL is £123 per week (£6,396 annually).

If your main job pays less than this threshold, your employer cannot legally stop you from having a second job or side business, regardless of what the contract says.

However, if you earn above this threshold—a category covering the vast majority of full-time professionals—the exclusivity clause may be enforceable, provided it is reasonable and necessary to protect the employer's legitimate business interests.

You must check if your contract demands "exclusive service." If it does, and you earn above the LEL, you are technically in breach of contract the moment you start trading.

2.

Non-Compete Clauses

These clauses are designed to prevent you from working for a competitor or setting up a competing business.

While these are usually associated with leaving a job, they often apply during employment too.

The enforceability of a non-compete clause relies on it being reasonable in scope.

A clause that bans you from "working in any capacity for any competitor worldwide" will likely be struck down by a UK court as an unlawful restraint of trade.

However, a clause that prevents you from "providing similar services to direct clients of the employer within a 10-mile radius" is much more likely to be upheld.

If your side hustle operates in the same industry as your day job, you are walking into a legal minefield.

3.

Conflict of Interest and Fiduciary Duty

Even if your contract does not explicitly ban side hustles, you are bound by an implied duty of fidelity and good faith.

This means you must act in the best interests of your employer.

A conflict of interest arises if your side hustle compromises your ability to do your main job, or if you exploit opportunities that rightfully belong to your employer.

For example, if you work in marketing for a large agency and start a freelance marketing consultancy on the side, you could be accused of poaching clients or diverting business opportunities that the agency would have otherwise captured.

Intellectual Property: Who Owns Your Output?

For those in creative, technical, or knowledge-based industries, Intellectual Property (IP) rights are a critical battleground.

Under the Copyright, Designs and Patents Act 1988, the employer is usually the first owner of copyright in work produced by an employee during the course of their employment.

The ambiguity lies in the phrase "course of employment."

If you use company equipment (laptops, software licences, workshop tools) to create your side hustle product, your employer may have a claim to the IP.

Furthermore, many contracts contain "moonlighting clauses" or specific IP assignment clauses that extend ownership of *all* inventions or creations made during the term of employment, even if created at home on your own time.

This is particularly common in software development and engineering.

If you are building a software product, writing code, or designing products, you must ensure you are not inadvertently gifting your business to your employer.

If your contract states that the company owns "all inventions created by the employee," and you build a prototype on a Saturday afternoon, legal ownership could default to your employer.

Tax Structures: Sole Trader vs.

Limited Company

Once you have cleared the contractual hurdles, you must choose a legal structure.

This decision impacts your tax liability, administrative burden, and the level of privacy you enjoy.

For side hustlers, the choice usually boils down to operating as a sole trader or forming a limited company.

Sole Trader Status

This is the simplest structure.

You are self-employed, and the business is not a separate legal entity from you.

You pay Income Tax and National Insurance on your profits via Self Assessment.

The administrative burden is low, but your privacy is limited; your name and business nature are on the public register.

Crucially, if your side hustle incurs debt, your personal assets (including your salary from your main job) are at risk.

Limited Company

A limited company is a separate legal entity.

It offers "limited liability," meaning your personal assets are generally protected if the business fails.

It can also be more tax-efficient if your side hustle profits exceed £30,000-£40,000, allowing you to take a small salary and dividends.

However, it comes with strict statutory obligations: filing annual accounts with Companies House, filing a Corporation Tax return with HMRC, and maintaining a register of people with significant control (PSC).

The Trading Allowance and Tax Thresholds

Understanding the tax thresholds is vital to ensuring your side hustle remains profitable.

The UK operates a progressive tax system, and your side hustle income is added to your employment income to determine your total tax liability.

The £1,000 Trading Allowance

If your gross turnover (total sales before expenses) from self-employment is £1,000 or less in a tax year, you are eligible for the Trading Allowance.

This allows you to earn this amount tax-free without even reporting it to HMRC, provided you have no other allowable expenses to claim.

If your turnover exceeds £1,000, you can choose to deduct the £1,000 allowance from your turnover instead of deducting actual expenses, but you must then register for Self Assessment.

The trade-off here is simple: if your expenses are low (e.g., a freelance writer working from home with no stock), claiming the £1,000 allowance is often more beneficial than calculating actual expenses.

If your expenses are high (e.g., buying stock, renting a studio), calculating actual expenses will likely yield a lower tax bill.

The Personal Allowance Trap

For the 2024/25 tax year, the standard Personal Allowance is £12,570.

Most employees use up this allowance through their salary.

Therefore, every pound you earn from your side hustle (after expenses) will be taxed at your marginal rate—20% for basic rate taxpayers, 40% for higher rate taxpayers.

You must also pay Class 2 and Class 4 National Insurance contributions if your profits exceed certain thresholds.

A common mistake is failing to account for "Payments on Account." If your Self Assessment tax bill exceeds £1,000, HMRC requires you to make advance payments towards the next year's tax.

This means in your first year of profitable trading, you could be paying 150% of your tax liability (100% for the current year + 50% advance payment), creating a significant cash flow shock.

Practical Checklist: Are You Ready to Launch?

Before you take the plunge, run through this checklist to ensure you haven't missed a critical legal or financial step.

If you cannot tick all the boxes, you may be exposing yourself to unnecessary risk.

• ✅ I have read my full employment contract, including staff handbooks referenced within it.
• ✅ I have checked for Exclusivity, Non-Compete, and IP assignment clauses.
• ✅ I have verified that my side hustle does not compete directly with my employer's services.
• ✅ I have confirmed I will not use company equipment or software for side hustle activities.
• ✅ I have calculated my projected turnover to check against the £1,000 Trading Allowance.
• ✅ I have registered for Self Assessment with HMRC (if turnover expected to exceed £1,000).
• ✅ I have set aside a reserve fund for "Payments on Account" tax bills.
• ❌ I have not assumed that "it's only a hobby" exempts me from tax rules.
• ❌ I have not used my work email address or phone number for side hustle clients.

Managing the Time and Energy Trade-off

While not strictly a legal restriction, the practical management of your time is often policed by your employer through performance reviews.

If your side hustle leaves you exhausted and your performance in your day job suffers, your employer is within their rights to manage this through capability procedures.

This is the "soft" restriction that catches many side hustlers out.

You must maintain a strict separation.

Use a separate phone number and email address.

Never work on your side hustle during your contracted hours, even if you are on a break.

Checking freelance emails on a work computer can be a disciplinary offence if it breaches IT usage policies.

The time you invest in your side hustle must come from your own time, not your employer's.

Insurance and Liability

If your side hustle involves interacting with the public, selling physical goods, or providing professional advice, you need insurance.

Your employer's insurance will not cover you for activities outside of your employment contract.

Public Liability Insurance

This covers you if a member of the public is injured or their property is damaged because of your business.

For example, if you are a dog walker and a dog bites a passerby, or you sell candles that cause a fire.

Costs vary, but for a low-risk side hustle, you can often secure cover for £50-£100 per year.

Professional Indemnity Insurance

If you offer advice or services (consulting, accountancy, marketing), this covers you if a client suffers a financial loss due to your negligence.

This is essential for knowledge-based side hustles and typically costs between £100 and £300 annually depending on the level of cover required.

What to Do If You Breach Your Contract

If you discover that your contract contains a restrictive clause that prohibits your side hustle, you have three options: stop the activity, ask for a variation of contract, or take the risk.

Stopping is the safest option but least appealing.

Asking for a variation is the professional route.

Many employers are reasonable if the side hustle does not compete and does not impact performance.

You can propose a formal side hustle policy or a specific waiver.

Taking the risk is the path of most resistance.

If you are caught, you could face a verbal warning, written warning, or final written warning.

In severe cases, particularly involving conflict of interest or IP theft, you may be summarily dismissed for gross misconduct without notice pay.

Furthermore, your employer could seek an injunction to stop you continuing the side hustle and sue for any profits you made that rightfully belonged to them.

"An employee who sets up a business in competition with his employer, or who diverts business opportunities to himself, commits a fundamental breach of the duty of fidelity.

This is so even if the business has not yet started to trade, provided the steps taken are more than mere preparation." — Legal Principle established in Hivac Ltd v Park Royal Scientific Instruments Ltd [1946]

Funding and Cash Flow Management

Funding a side hustle while employed is distinct from funding a full-time startup.

Banks are often more willing to lend to you because you have a stable income, but you must be careful not to cross financial lines.

Using a personal credit card or personal savings is the most common route.

However, if you need external funding, be aware that business loans often require a personal guarantee.

If your side hustle fails, you are personally liable for the debt.

Since you are employed, lenders will pursue your salary.

Avoid the mistake of mixing funds.

Open a separate business bank account.

Even as a sole trader, this is critical for two reasons: it makes filing your Self Assessment tax return infinitely easier, and it protects you from "piercing the corporate veil" if you are a limited company director.

If you mix personal and business funds, you risk HMRC investigating your personal finances more closely, and you lose the protection of limited liability.

Conclusion: The Exit Strategy

Running a side hustle while employed is a juggling act that requires legal literacy and financial discipline.

The restrictions in your contract are not just words on paper; they are enforceable obligations that can derail your plans if ignored.

The most successful side hustlers are those who operate transparently with their employers, keep meticulous tax records, and maintain a strict separation between their day job duties and their entrepreneurial ambitions.

Before you start, read the contract.

Understand the non-competes.

Check the IP clauses.

Register for Self Assessment.

Set aside tax.

If the side hustle grows to the point where it threatens your performance or conflicts with your main job, you have reached the pivot point: it is time to negotiate a reduction in hours or resign to go full-time.

Until then, protect the primary income source that funds your dream.