A private hire driver, a flat weekly fee, and a single phrase in a set of regulations from the year 2000. The Supreme Court has just settled an argument that has run through the tribunal system for years, and the answer makes it meaningfully easier for part-time workers to win.

Employment law cases rarely turn on something as small as this. One phrase, four words long, sat in a set of regulations for over two decades without a definitive answer to what it actually meant. The Supreme Court has now given that answer, and it changes the odds for every part-time worker bringing a discrimination claim from here on.

Warren Augustine worked as a private hire driver for Data Cars Limited, a small taxi firm, on a part-time basis. Like every driver at the company, he was required to pay a flat weekly circuit fee of £148 to access the firm's booking system, regardless of how many hours he actually worked.

For a full-time driver working long hours, that fee is spread across a large number of jobs and a large amount of earning potential. For a part-time driver like Mr Augustine, the same flat fee represented a proportionally much heavier cost relative to what he could actually earn. He argued the fee should have been applied pro rata, in line with his part-time hours, and that charging him the same flat amount as a full-time driver amounted to unlawful less favourable treatment under the Part Time Workers Regulations 2000.

Regulation 5 of those regulations gives part-time workers the right not to be treated less favourably than a comparable full-time worker, but only where two conditions are met: the treatment must be on the ground that the worker is part-time, and it must not be objectively justified.

The entire case turned on that first condition, and specifically on three words: "on the ground that." Did that phrase mean part-time status had to be the sole reason for the less favourable treatment, or was it enough for part-time status to be one effective cause among others?

This was not a new question. Courts had wrestled with it for years, and a Scottish case called McMenemy v Capita Business Services Ltd had previously held that part-time status needed to be the sole cause. The Employment Tribunal in Mr Augustine's case followed that approach, finding that while he genuinely was treated less favourably, the flat fee existed because it was standard industry practice, not solely because he worked part-time. His claim was dismissed. The Employment Appeal Tribunal agreed it was bound by McMenemy, though it openly said it thought that earlier decision was wrong in law, and gave Mr Augustine permission to appeal further. The Court of Appeal upheld the dismissal too. That left the Supreme Court to settle it properly.

The Supreme Court sided with Mr Augustine, and in doing so overturned McMenemy entirely.

The reasoning is genuinely elegant. The equivalent European Union legislation behind these regulations used the phrase "solely because" when describing when part-time workers are protected. When the UK government drafted its own domestic regulations, it deliberately chose different, looser wording: "on the ground that." The Supreme Court held that this was not an accident. Parliament could have copied the EU's stricter "solely because" language directly. It chose not to, and that choice meant the UK regulations were always intended to offer broader protection than the EU minimum required.

The court also pointed to how "on the ground that" is interpreted everywhere else in discrimination law, where a protected characteristic only needs to be an effective cause of less favourable treatment, not the only one. Bringing part-time worker protection into line with that general principle, rather than treating it as some stricter, separate standard, was the more coherent reading of the law.

The upshot: a part-time worker no longer has to prove that being part-time was the only reason they were treated worse. They only need to show it was a genuine, effective contributing cause, even where other factors, such as standard industry practice or administrative convenience, were also in play.

This is not a small technical shift. Requiring a claimant to prove sole causation is an extremely high bar, because almost every employer can point to some other contributing reason for a policy, standard practice, cost, administrative simplicity, and under the old test, that alone was often enough to defeat a claim entirely. Under the new test, those other reasons do not disappear from the case. They simply move to a different, later question: whether the treatment was objectively justified, and how much compensation should follow, rather than whether the claim succeeds at all.

The Supreme Court was explicit that the burden of proof still sits with the employer to explain the actual ground for the treatment. Combined with the lower causation threshold, this means employers can expect their reasoning to face considerably closer scrutiny going forward, and tribunals now have more scope to infer a prohibited reason where the employer's explanation does not fully add up.

You do not need to be heading into an employment law career for this case to be worth understanding. It is a genuinely clean example of a skill every solicitor needs: taking a handful of words in a piece of legislation and working out what Parliament actually intended by comparing it against the wording it deliberately chose not to use.

That kind of close statutory interpretation shows up constantly, in property law, in company law, in contract disputes, in almost every practice area you could end up in. This case is a textbook illustration of the technique, and a genuinely good one to reference if you are ever asked in an interview to talk about a case that shows you understand how courts actually reason through legislation, rather than simply memorising the outcome.

A flat fee, a part-time driver, and a single overturned precedent have just made it meaningfully easier for part-time workers across the country to bring a successful discrimination claim. The lesson underneath the headline is the one worth carrying forward: sometimes the biggest legal shifts come not from a dramatic new law, but from a court finally deciding what a handful of quiet, ordinary words in an old piece of legislation were actually supposed to mean.

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