Augustine v Data Cars is now the leading authority on the rights of part-time workers. The Supreme Court held on 12 August 2026 that part-time status need only be an effective cause of less favourable treatment to engage regulation 5 of the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000, and disapproved the stricter sole-ground test that had governed tribunals across Great Britain since 2007. Ten years of litigation ends in the driver’s favour.
What did the Supreme Court decide in Augustine v Data Cars?
Lady Simler gave the only judgment, with Lord Lloyd-Jones, Lord Hamblen, Lord Leggatt and Lord Richards agreeing. The court allowed the appeal. Warren Augustine drove for Data Cars as a part-time private hire driver from 2016, averaging a little under 35 hours a week against comparator drivers working far longer, and every driver paid the company a flat circuit fee of £148 a week for access to its booking and dispatch system regardless of hours worked. His complaint was arithmetic as much as legal. A fixed weekly charge consumes a larger share of a part-time driver’s earnings, so identical treatment produced unequal burdens. The judgment in [2026] UKSC 30 holds that this engages the 2000 Regulations if part-time status was an effective cause of the disadvantage, even where it was never the sole reason for the charging structure.
Why was McMenemy disapproved?
The obstacle throughout was McMenemy v Capita Business Services, a 2007 decision of the Inner House of the Court of Session requiring part-time status to be the sole ground of the treatment. The employment tribunal dismissed Mr Augustine’s claim. The Employment Appeal Tribunal then concluded in 2024 that the effective-cause approach was correct in principle, yet held itself bound to follow McMenemy because its own jurisdiction runs across Great Britain and a single rule was needed. The Court of Appeal divided on the question in 2025 and likewise dismissed the appeal, leaving the Supreme Court to settle a conflict that had persisted, remarkably, for the best part of two decades across three levels of tribunal and court. Lady Simler’s reasoning was direct. When the 2000 Regulations were made, the phrase “on the ground that” already carried a clear and authoritatively established meaning in domestic discrimination law: a prohibited ground could substantially influence treatment without being the main reason, still less the only one. Parliament’s drafters did not reproduce the “solely because” wording of the European framework agreement. That omission was deliberate, and the effective-cause case law was to be followed.
What should employers audit now?
Flat fees are the immediate exposure. Any fixed charge, deduction or allowance applied uniformly to part-time and full-time staff now founds a claim on the easier causation test, because uniformity is precisely what produces the pro rata disadvantage. For law firms that reaches fixed contributions to practising costs, per-head charges, chambers rents and threshold-based benefits, and objective justification becomes the battleground rather than causation. Advice given on the sole-ground footing since 2007 needs revisiting. The Supreme Court case page records how narrow the disputed question was, yet its consequences are wide: commentators were describing the decision as floodgates-opening within hours of hand-down, and tribunals in England, Wales and Scotland now apply one rule. Belief-discrimination litigation has already reshaped employment risk this summer, as our report on University of Bristol v Miller set out, and causation is loosening at the same time. Employers tracking the wider reform picture can follow our Employment Rights Act implementation tracker for the statutory changes arriving alongside the case law.
Any employer applying a flat fee, deduction or allowance to part-time and full-time staff alike now faces the effective-cause test rather than the sole-ground test. Causation will rarely defeat these claims again. Objective justification, evidenced and documented, is where these disputes will now be won or lost, and ten years of contrary advice needs reviewing.