Treated worse because you work part time? What the Supreme Court's Augustine ruling changes

Updated 23 September 2026

For almost twenty years, an appeal court in Scotland, and tribunals across Great Britain that felt bound to follow it, read the part-time workers rules as covering only treatment caused solely by working part time. Any other reason in the mix could sink a claim. The Supreme Court has now said that was wrong. If you work fewer hours than full-time colleagues and are paid, charged or treated in a way that leaves you worse off, this is what the ruling means, what your employer can still argue, and how the deadline works.

What the Supreme Court decided

The case is Augustine v Data Cars Ltd [2026] UKSC 30. Five justices heard it and the decision was unanimous. Lady Simler gave the judgment of the court, which ends with this sentence: the 2000 Regulations prohibit less favourable treatment of part-time workers "where their part-time status is an effective cause of the impugned treatment. It need not be the sole cause."

That settles a question the courts had disagreed on since 2007. The court said the words the government chose in the regulations, "on the ground that", already had a settled meaning in discrimination law by the time the rules were written in 2000. If the protected reason had a significant influence on the treatment, or was an effective cause of it, that was enough. The protected reason did not have to be the main reason, let alone the only one.

The court's press summary gives the short version of the reasoning, and the full judgment is published by The National Archives.

The case: a flat fee and a driver on fewer hours

Warren Augustine was a private hire driver for Data Cars Ltd, a small business, and worked for it as an employee in 2016. According to the judgment, he averaged 34.8 hours a week. Full-time drivers worked more than 43 hours, and some more than 60.

Every driver paid the same weekly "circuit fee" of £148 to use the company's booking and dispatch system, whatever their hours. Because Mr Augustine drove fewer hours, the fee took a bigger bite out of each hour he worked. He paid more per hour to drive than his full-time comparator and took home less per hour as a result.

He claimed that was less favourable treatment because he was part-time. The case then went through four levels:

• Employment tribunal: rejected the claim. It said the fee was charged so the business could earn revenue, not because he was part-time, and that in any case part-time status was not the "sole ground" for it.
• Employment Appeal Tribunal ([2024] EAT 117): applied the pro rata principle and found that the fixed fee was less favourable treatment. But part-time status was not the only reason, and the EAT considered itself bound by an earlier Scottish decision requiring a sole cause, so the appeal failed.
• Court of Appeal ([2025] EWCA Civ 658): the majority, Bean and Edis LJJ, thought the right test was effective cause, but also felt bound by the Scottish decision. Elisabeth Laing LJ would have kept the sole-cause test. The case then went to the Supreme Court to settle the point for the whole of Great Britain.
• Supreme Court, 12 August 2026: appeal allowed, unanimously.

Why "sole cause" was the rule until now

The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 were made to put an EU directive into UK law. The directive gave effect to a framework agreement on part-time work, and clause 4.1 of that agreement says part-time workers must not be treated less favourably than comparable full-time workers "solely because they work part time" unless the difference is objectively justified.

In 2007, in McMenemy v Capita Business Services Ltd, the Inner House of the Court of Session in Scotland read the UK regulations as if they carried that same "solely" test. A year later, in Sharma v Manchester City Council, the Employment Appeal Tribunal in England took the opposite view: if being part-time was one of the reasons, that was enough. The two lines of authority sat side by side, and because McMenemy was an appeal court decision, tribunals and the EAT tended to follow it.

The Supreme Court sided with Sharma. Its main points were these:

• The UK regulations do not contain the word "solely". The government used the phrase "on the ground that", which already had an established meaning in UK discrimination law. The court said the obvious implication is that this was deliberate.
• Even if the EU agreement set a narrow test, the UK was free to give part-time workers more protection than the minimum. The power used to make the regulations, section 19 of the Employment Relations Act 1999, was broad enough for that.
• The word "only" in regulation 5(2) does not qualify the causal link, and the singular word "ground" just reflects that part-time status is the one protected characteristic in play.
• Requiring a sole cause would clash with the standard approach to causation in discrimination cases and risk uncertain and unreasonable outcomes.

What the ruling changes for part-time workers

In practice, it removes an easy defence. Most decisions about pay, fees, bonuses, overtime or shifts have more than one reason behind them. Before this ruling, an employer could often defeat a part-time worker's claim by pointing to any other reason, such as revenue, a software limit, or a policy that happened to apply to everyone. Under the sole-cause test, that was frequently the end of it.

Now the question is simpler: was being part-time an effective cause of the worse treatment? If it was, the right in regulation 5 applies, and the argument moves on to whether the employer can justify it.

The ruling also confirms a point that matters for flat-rate charges and payments. The regulations tell tribunals to apply the pro rata principle unless it is inappropriate, and the court described it as the presumptive way of deciding whether treatment is less favourable. A charge or payment that is the same in pounds for everyone can still leave a part-time worker worse off once it is measured against hours.

Situations where this is likely to come up include:

• Fixed fees or deductions charged per week or per month regardless of hours, like the circuit fee in this case.
• Bonuses, allowances or benefits that are not pro-rated, or pro-rated in a way that shortchanges part-timers.
• Training, promotion or selection rules that part-time staff cannot meet because of their hours.
• Redundancy selection criteria that count hours or availability in a way that marks part-timers down.

Each of these still depends on the facts, on a proper comparator, and on justification. The ruling does not make every difference unlawful. It stops a claim failing simply because there was another reason as well.

What the law actually gives you

The core right is in regulation 5. A part-time worker has the right not to be treated less favourably than the employer treats a comparable full-time worker, either in the terms of the contract or by being subjected to any other detriment. The right applies only if the treatment is on the ground that the worker is part-time, and only if it is not justified on objective grounds.

Who is covered. The regulations protect workers, not just employees. Regulation 1 defines a worker as someone working under a contract of employment or any other contract to do the work personally, where the other party is not their client or customer. If you are not sure which you are, our guide to worker and employee status explains the difference.

The comparator. Under regulation 2, you compare yourself with a full-time worker employed by the same employer, under the same type of contract, doing the same or broadly similar work, with regard where relevant to qualifications, skills and experience. The comparator should work at the same establishment, or at a different one if nobody suitable works at yours. A hypothetical full-time worker will not do, which is why picking the right comparator is often the first practical question.

The pro rata principle. Where a comparable full-time worker gets pay or another benefit, the part-time worker should get at least the proportion of it that matches their weekly hours. Acas gives a simple example: if a full-time role pays £28,000 a year, someone doing the same role for half the hours should get £14,000. The same logic applies to holiday, sick pay and other benefits.

Overtime. Regulation 5(4) is an exception. Paying a part-timer a lower rate for extra hours is not less favourable treatment where their total hours, including those extra hours, do not exceed the full-time worker's normal hours. Enhanced overtime rates usually only have to kick in once you pass full-time hours.

What your employer can still argue

The ruling makes the first hurdle easier. It does not remove the defence. Under regulation 5(2)(b), the right applies only if the treatment is not justified on objective grounds, and that is where much of the argument will now take place.

The Supreme Court said the other causes an employer points to are better seen as possible justifications than as reasons that stop the right arising at all. In this case it mentioned the need to earn revenue and limits in the booking software as examples of the kind of thing an employer might raise. The other causes may also affect how much compensation is awarded.

The judgment also noted that Mr Augustine's chosen comparator worked more than 90 hours a week. The court said that the hours worked over and above a standard full-time week of 43.17 hours might properly be considered when deciding what, if any, compensation should be awarded.

So the ruling decided the legal test. It did not decide that Mr Augustine wins his claim, and it did not decide that flat fees are always unlawful. Justification is fact-specific, and an employer with a genuine, proportionate business reason can still succeed.

The deadline: three months now, six months from 1 October

Complaints under the regulations go to an employment tribunal under regulation 8. Today the time limit is three months from the date of the less favourable treatment, or from the last act if it is part of a series of similar acts. A tribunal can hear a late claim if it thinks it just and equitable, but you should never plan on that.

That changes on 1 October 2026. The Employment Tribunal (Extension of Time Limits) (Miscellaneous Amendments and Transitional Provisions) Regulations 2026 replace the three months in regulation 8 with six months. Regulation 10 says the longer limit applies only where the treatment, or the last act in a series, happens on or after 1 October 2026.

• Treatment before 1 October 2026: three months, as now.
• Treatment on or after 1 October 2026: six months.
• A continuing series: the date of the last act decides which limit applies.

A flat fee charged every week, or a pay term applied every month, may be a series of acts, but whether it is depends on the facts. The safe approach is to count from the earliest date that could matter. Our tribunal deadline calculator applies the 1 October switch for you.

Before you can claim, you must contact Acas for early conciliation. Complaints under regulation 8 are listed in section 18(1) of the Employment Tribunals Act 1996, so the usual rule applies, and starting early conciliation pauses the clock. Our step-by-step guide to starting Acas early conciliation shows how.

How to raise it, step by step

1. Work out the comparison. Identify a full-time colleague on the same type of contract doing the same or broadly similar work. Write down what they receive or pay, and what you receive or pay, and convert both to a per-hour figure.
2. Ask for the reasons in writing. Regulation 6 lets you request a written statement of the reasons for the treatment. Your employer should provide it within 21 days. If they deliberately do not answer without a reasonable excuse, or give an evasive or equivocal one, a tribunal can draw inferences, including that they broke the rules.
3. Raise a grievance if it helps. A written grievance can fix the problem without a claim. It does not pause the deadline. Our guide to raising a workplace grievance covers what to put in it.
4. Diary the deadline. Three months for treatment before 1 October 2026, six months for treatment on or after it, counting from the treatment or the last act in a series.
5. Contact Acas before the deadline, even while a grievance or a request for reasons is still running.

You are also protected for using these rights. Under regulation 7, it is automatically unfair to dismiss an employee because they brought a claim, asked for a written statement, alleged a breach, or refused to give up a right under the regulations. Workers are protected from any other detriment for the same reasons. The protection does not apply to an allegation that is false and not made in good faith.

What you can get, and the sex discrimination angle

If a tribunal upholds the complaint, it can make a declaration, order compensation, and recommend action. Compensation is whatever it considers just and equitable, taking into account the breach and any loss caused by it, including expenses and lost benefits. Regulation 8 rules out compensation for injury to feelings in a claim under regulation 5, so these awards tend to track the money actually lost.

There is often a second route. As Acas points out, women are more likely to work part time than men, so a rule that disadvantages part-timers can amount to indirect sex discrimination under the Equality Act 2010. That claim works differently, with its own tests and its own remedies. Our page on the discrimination claim time limit covers the deadline, which also moves to six months for acts on or after 1 October 2026. Whether to bring one claim or both is exactly the kind of decision to take advice on.

If your hours are low or unpredictable, the zero-hours reforms may also be relevant, and if you want to change your hours, our flexible working request template covers the statutory route.

This page is general information for England, Wales and Scotland, not legal advice. For your own situation, speak to Acas, a solicitor, or your union.