Supreme Court issues landmark ruling on part-time worker protections

The UK Supreme Court has ruled that part-time status need only be an effective cause of less favourable treatment, and not the sole cause.

The landmark ruling could have far-reaching implications for the application of legal protections for part-time workers, according to lawyers.

In the case of Augustine v Data Cars, taxi driver Warren Augustine first brought a claim against his employer in 2016.

During his employment, he had to pay Data Cars a "circuit fee" of £148 a week for access to its booking and dispatch system, alongside an equipment rental fee of £12. This fee was the same for all drivers, regardless of working full- or part-time.

Augustine also rented a vehicle from the company, he had to acquire a certain level of insurance in line with Transport for London requirements, and he needed to valet the car regularly.

He argued that the circuit fee was contrary to Regulation 5 of the Part-Time Workers' Regulations as part-time workers would be paying a higher fee per hour worked than their full-time counterparts.

The initial tribunal ruled that the vehicle rental payments and having to wear a uniform fell outside of national minimum wage regulations, but payments for insurance and valeting could be deemed valid employment expenses.

The Employment Appeal Tribunal ruled that uniform and rental expenses were directly connected to his employment, suggesting that the initial tribunal had erred.

The EAT also referred to a decision in McMenemy v Capita Business Services, which held that Regulation 5 only applies if the employer intends to treat the worker less favourably for the sole reason they are part-time.

In May 2025, his case was dismissed again at the Court of Appeal, which ruled that - although the Part Time Workers' Regulations include the term "solely" - it believed this indicated that part-time status would need to be the predominant reason for unequal treatment.

The case was then referred to the Supreme Court to resolve this inconsistency, and the court has today agreed that part-time status needs to be an "effective" cause, but does not have to be the sole one.

Implications for employers

Clare Brennan, partner at Hunters Law, said the decision did not necessarily mean a narrowing of protections for part-time workers, and advised employers to remain cautious.

"The Supreme Court has confirmed that part-time status need only be an effective cause of less favourable treatment, not the sole cause," she explained.

"However, the Court has also recognised that not every disadvantage experienced by a part-time worker will necessarily amount to unlawful treatment.

"This is one of those rare cases where the employer won the litigation but the employee won the legal argument."

Katie Maguire, partner at Devonshires, said the ruling could "open the floodgates" to a large number of potential claims against employers in sectors where part-time working is more prevalent.

"Part-time workers will now only need to show that their part-time status was one of the operative reasons for the treatment they received, rather than being the sole or predominant reason," she explained.

"For employers, they now need to demonstrate far more disciplined documentation of decision-making in regard to part-time staff, particularly around pay enhancements, bonus eligibility, overtime access and shift allocation."

Employers will also need to ensure that "any and all decisions" affecting part-time workers are clearly evidenced, consistently applied and free from assumptions about someone's availability or commitment, she added.

"In an environment where staffing models are complex and decisions are rarely attributable to a single factor, tribunals will now need to analyse decision-making far more broadly in terms of the range of factors that contributed to a decision and whether part-time status was one of them. HR and legal teams may need to adjust the rationale of their mixed-motive decisions as a result.

"Employers have arguably been left with more questions than answers in the immediate aftermath of the judgment. The key message for employers is that the distinction between a decision being about part-time status and part-time status simply being one factor in a wider business decision has become much more important."