Court of Appeal confirms the correct approach to causation with part-time workers claims

In this blog we consider the impact of the very recent Court of Appeal decision on part-time workers claims. In Augustine v Data Cars [2025] EWCA Civ 658, the Court of Appeal confirms the correct approach to causation when dealing with such claims

In Augustine, the Court of Appeal upheld the Employment Appeal Tribunal’s decision where Eady J held that the correct way to approach causation under the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 (“PTWR”) was to apply the “sole cause” test, as set out in the Court of Session (Inner House) decision of McMenemy v Capita Business Services Limited [2007] IRLR 400. As a result, the broader “effective cause” test favoured by EAT decisions such as Sharma v Manchester City Council [2008] ICR 623 and Carl v University of Sheffield [2009] 3 CMLR 21 are no longer to be followed.

Lucas Nacif of Farore Law earlier this year acted as counsel for the appellant in the EAT decision of Mireku v London Underground Limited [2025] EAT 57, where he argued that the EAT should depart from the EAT decision of Augustine v Data Cars and adopt the “effective cause” test instead. This is primarily because, he argued, the “sole cause” test would undermine the protection of part-time workers against discrimination (see blog here). In Mireku, the EAT concluded that it was not desirable to depart from the previous EAT decision of Augustine v Data Cars Ltd, mentioned above.

This blog now examines the Court of Appeal’s decision and its implications.

The Court of Appeal decision and what to take away

All three Court of Appeal Judges decided that McMenemy should be followed, that is the “sole cause” test should be applied for causation, and this is the test that should be applied for now. However, they gave leave to appeal to the Supreme Court because the majority of the Court of Appeal indicated that they believe McMenemy is wrong, but it would take the Supreme Court to decide the point.  The Supreme Court has to decide this point because only the Supreme Court can overturn a Court of Session decision.

It is notable that Edis LJ (as part of the majority) said that a purposive construction to the PTWR would lead to a “broader, rather than narrower class of potential beneficiaries of the new remedy…and this is reinforced by the extract from the Explanatory Notes to the [Employment Relations Act 1999] which states its aim as being “to remove discrimination against part-timers and improve the quality of part-time work””. Edis LJ went on to state that it is hard to think of any good reasons why the PTWR should be narrowly construed, noting that the word “solely” from the underlying EU Directive was deliberately omitted from the regulation 5 PTWR. We, at Farore Law, happen to agree!

In addition, Bean LJ observed that the words “on the ground that” (in regulation 5(2)(a) PTWR) was a phrased similarly deployed in other anti-discrimination statutes, such as the Sex Discrimination Act 1975, where the courts have held that the correct approach to causation is to apply the “effective and predominant cause” or the “real and efficient cause” test. We believe that there is a good deal of force in this argument.

It is highly likely that there will be a Supreme Court hearing in the near future on Augustine, providing a conclusive view on the issue of causation. If we were betting people, the Supreme Court will decide that the causation test should be “effective cause”.

The “sole cause” test will pose significant problems for claimants in the meantime. As noted by Eady J in Augustine v Data Cars [2024] EAT: “discrimination against part-timers will often take place because of factors associated with their part-time status; limiting the protection to less favourable treatment solely on the ground of part-time work risks excluding such cases, where the part-time nature of the work might be the effective, but not the sole, reason for that treatment”. Indeed, it is of note how both the EAT and the Court of Appeal’s majority in Augustine chose to follow McMenemy with reluctance.

Given these issues, it is hoped that the Supreme Court can provide an authoritative resolution into how causation under the PTWR should be approached. Claimants would be advised to seek a stay of their cases, where they are predominantly or materially concerned with discrimination in the grounds of part-time worker status, pending the outcome of the Supreme Court decision.