Supreme Court Makes It Easier for Part-Time Workers to Claim Discrimination

A Supreme Court ruling handed down this summer has quietly lowered the bar for part-time workers bringing a discrimination claim against their employer — and it applies to any business with a mix of full-time and part-time staff, not just the taxi industry the case came from. This guide explains what changed in Augustine v Data Cars Ltd, and what it means for how you treat part-time employees.

A quick explainer of the terms you’ll see

Part-Time Workers Regulations 2000 (PTWR) — the UK law giving part-time workers the right not to be treated less favourably than a comparable full-time worker, unless the employer can objectively justify the difference.
Less favourable treatment — any way a part-time worker is treated worse than a full-time comparator — in pay, benefits, terms, or how they’re managed.
Causation — the legal question of whether the reason for someone’s treatment was actually their part-time status, as opposed to some other factor.
Sole cause vs effective cause — two different legal tests for causation. “Sole cause” means part-time status had to be the only reason for the treatment — a high bar. “Effective cause” means it only had to be a genuine contributing reason, even alongside other factors — a much easier bar to clear.
Supreme Court — the highest court in the UK, whose rulings bind every lower court and tribunal.

What happened in the case

Mr Augustine worked part-time as a private hire driver for Data Cars. Like all drivers, he was charged a flat weekly “circuit fee” of £148 for access to the company’s booking and dispatch system — the same fee regardless of whether a driver worked full-time or part-time hours.

Because the fee was fixed rather than scaled to hours worked, Mr Augustine argued that he effectively paid a higher fee per hour driven than a comparable full-time driver — and that this amounted to less favourable treatment because he was a part-time worker.

The Employment Tribunal accepted the fee was the same for everyone, but rejected the claim on the basis that the fee wasn’t charged solely because he was part-time — it was a flat charge applied to all drivers, full-time or not. The Employment Appeal Tribunal, though it thought the earlier case it was bound by had been wrongly decided, felt unable to depart from it, and the claim failed again.

The case reached the Supreme Court specifically to resolve this point: does a worker have to prove part-time status was the only reason for their treatment, or is it enough that it was a genuine contributing reason?

What the Supreme Court decided

The Supreme Court unanimously allowed the appeal, ruling that part-time status only needs to be an effective cause of the less favourable treatment — not the sole cause. This brings the causation test for part-time worker claims in line with the test already used in other types of discrimination claim, where a contributing factor has generally always been enough, without needing to be the only one.

In practical terms: a flat fee, policy, or practice that isn’t explicitly aimed at part-time workers can still amount to unlawful less favourable treatment, if part-time status is genuinely one of the reasons it disadvantages them — even where other factors are also in play.

Why this matters for your business

This ruling makes it meaningfully easier for a part-time worker to succeed in a discrimination claim, because the previous “sole cause” test was a genuinely difficult bar to clear — most real workplace situations involve more than one contributing factor, so requiring part-time status to be the only one let a lot of arguably unfair treatment through.

Crucially, this isn’t limited to fees or pay. The same reasoning applies to any policy or practice that, in effect, disadvantages part-time staff compared to full-time colleagues — even where that wasn’t the specific intention. Common areas worth thinking about:

Flat fees or charges applied equally regardless of hours worked, which can work out disproportionately expensive per hour for part-time staff.
Access to training, development, or promotion opportunities, where part-time staff might be more easily overlooked even without any deliberate policy against them.
Benefits or perks structured around full-time patterns — for example, based on a minimum number of days worked, which part-time staff may struggle to reach even doing genuinely comparable value of work.
Scheduling and workload expectations that assume full-time availability as the default.

Remember, though, that this ruling is about the causation test only — it doesn’t remove an employer’s ability to justify a difference in treatment on objective grounds unrelated to part-time status. If you have a genuine, evidenced business reason for a policy, that defence still stands. What’s changed is that it will now be easier for a claim to get off the ground in the first place, putting more pressure on employers to have that justification ready and documented.

What employers should do now

Review any flat fees, charges, or fixed costs applied equally to full-time and part-time staff, and check whether they work out disproportionately for those working fewer hours.
Check benefits, training access, and development opportunities for any patterns that might unintentionally disadvantage part-time staff.
Where you do treat part-time and full-time staff differently, be ready to explain why — with a genuine, objective, documented business reason, not just historical practice.
Brief managers that a policy doesn’t need to be deliberately aimed at part-time workers to create risk — it’s the practical effect that matters now, not just the intention.
Don’t assume “we treat everyone the same” is automatically safe. As this case shows, treating everyone identically can itself produce less favourable treatment where the practical impact falls unevenly.

How Cheviot HR can help

This ruling raises the bar for how carefully policies affecting part-time staff need to be thought through. We can review your current terms, benefits, and policies for any patterns that could now carry more risk, and help you build genuine, defensible justifications where differences in treatment are truly necessary.

Get in touch at heidi@cheviothr.co.uk or visit https://cheviothr.co.uk to talk through what this means for your business.