A part-time private hire driver challenged a flat weekly fee his company charged for access to its booking and dispatch system. Because the fee did not vary with hours worked, part-timers paid far more per hour than full-timers for the same service. He claimed less favourable treatment because of his part-time status. The Employment Tribunal rejected the claim, finding the fee was a revenue measure and that part-time status had to be the sole reason for the treatment, with the resulting appeal leading all the way to the Supreme Court

The Supreme Court unanimously held that a part-time worker (PTW) bringing a less favourable treatment claim under the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations (PTWRs) 2000 does not need to prove that part-time status was the sole reason for the treatment. It is sufficient that it was an effective cause or significantly influenced the outcome. Employers can no longer defend a policy simply by pointing to a second commercial motive, such as administrative convenience or revenue generation. Neutral-looking practices like flat fees, fixed charges and benefit rules that fall harder on part-timers are now much easier to challenge, in your own organisation and among your clients.

The successful claim rested on Regulations 5(1) and 5(2) of the PTWRs. These were made under Section 19 of the Employment Relations Act 1999 to implement Directive 97/81/EC. Under the law, PTWs must not be treated less favourably than comparable full-timers unless the treatment is objectively justified. The Court stressed that the Regulations deliberately omit the words "solely because", so the ordinary "effective cause" approach from discrimination law applies.

To reduce your risk, review pay structures, fees and benefits for anything that costs part-timers proportionately more or gives them less, and pro-rate salary, bonuses, pensions, leave and expenses wherever possible. Where a policy does have a disproportionate effect, record the legitimate aim behind it and why it is necessary and proportionate, bearing in mind that revenue or convenience alone is unlikely to be enough. Remember that the Regulations cover workers as well as employees, so include contractors in your review. Finally, make sure HR, payroll and finance teams understand the new test, and treat any part-time grievance about pay or benefits as a potential claim by taking specialist advice early.