By Sara Meyer & Alex Lock
|Published 09 September 2026
In this case, the Supreme Court held that a worker alleging discrimination under the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 (the Part-Time Workers Regulations) need only show that their part-time status was an effective cause, and not necessarily the sole cause, of the less favourable treatment.
Under regulation 5(2) of the Part-Time Workers Regulations (Regulation 5(2)), a part-time worker's right not to be treated less favourably than a comparable full-time worker is stated to apply "only if (a) any treatment is on the ground that the worker is a part-time worker, and (b) the treatment is not justified on objective grounds".
The Part-Time Workers Regulations were intended to implement the EU Framework Agreement on part-time work, clause 4.1 of which refers to treatment “solely because” an individual works part-time.
Previous case law in England and Scotland has reached conflicting conclusions on whether regulation 5(2) should be interpreted to require the worker's part-time status to be the sole reason for the less favourable treatment, consistent with the wording of the EU Framework Agreement, or whether it is sufficient for part-time status to be an effective cause.
Mr Augustine was employed by Data Cars Ltd on a part-time basis. All drivers paid a weekly "circuit fee" to access the company's booking system. The fee was fixed at £148 per week regardless of hours worked. Workers who drove fewer hours therefore paid a higher fee per hour than those working longer hours. Mr Augustine claimed that this was less favourable treatment under Regulation 5(2).
The employment tribunal dismissed the claim, holding that even if Mr Augustine having to pay the fixed circuit fee meant he was treated less favourably than comparable full-time workers, his claim could not succeed as part-time status was not the sole reason for the treatment.
Both the EAT and the Court of Appeal considered that the tribunal's decision that part-time status had to be the sole reason for less favourable treatment was wrong in law. However, they considered themselves bound by an earlier decision of the Scottish Court of Session that had taken the opposite view. Mr Augustine appealed.
The Supreme Court allowed the appeal, confirming how Regulation 5(2) should be interpreted across Great Britain. It noted that the phrase "on the ground that" has an established meaning in discrimination law, namely that discrimination is established where the protected characteristic is a significant influence or effective cause of the treatment. It need not be the main cause and certainly need not be the sole cause. This meaning was already well understood by the time the Part-Time Workers Regulations were enacted.
It was unnecessary to determine the precise meaning of the phrase “solely because” in the EU Framework Agreement because there was nothing preventing the domestic legislation from providing more favourable protection than the minimum required by EU law.
The fact that the Part-Time Workers Regulations did not use the words “solely because” and instead adopted the phrase “on the ground that”, which already had a settled legal meaning in discrimination law, was significant. Had Parliament intended to impose a sole-cause test, it could easily have said so.
The Court also rejected arguments based on the wording of regulation 5(2). The word “only” did not qualify the causal link between the treatment and part-time status; rather, it indicated that both statutory conditions must be met, namely causation and the absence of objective justification. Nor did the singular use of the word “ground” indicate that there could be only one reason for the treatment.
Requiring part-time status to be an effective cause of the treatment is consistent with both the language and purpose of the Part-Time Workers Regulations. Limiting protection to situations where part-time status is the sole cause would risk excluding many cases in which part-time work is genuinely responsible for the disadvantage suffered. The Court gave the hypothetical example of an employer denying a benefit to "part-time workers over 6 feet tall", in which case there would be two reasons for the treatment, and it was hard to see why the position should not be the same as it is in discrimination law. The Court therefore held that Regulation 5(2) is engaged where part-time status is an effective cause of the less favourable treatment, even if other factors also contributed.
Importantly, the Court recognised that other causes of the treatment may be relevant when assessing whether the treatment was objectively justified or when determining compensation. However, their existence does not prevent a part-time worker's statutory right not to be treated less favourably than a comparable full-time worker from arising in the first place.
This case confirms that, for a claim under Regulation 5(2), claimants need only establish that their part-time status was an effective cause of the less favourable treatment, not the sole cause. Employers defending claims should therefore focus carefully on objective justification, to which their business reasons, operational constraints, and similar factors may all be relevant.
(Note, discrimination against part-time workers in Northern Ireland is governed by separate regulations. However, the wording of the relevant provision is the same. This decision should therefore also apply in Northern Ireland.)
