Part-time status must be ‘sole reason’ for less favourable treatment

The Employment Appeal Tribunal’s (EAT) decision in Mr J Mireku v London Underground Limited offers important guidance for employers on the interpretation of the Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 (PTWR). Read the legislation in full here.

This case clarifies a key principle: a part-time worker alleging less favourable treatment must prove that their part-time status was the sole reason for that treatment — not just a contributing factor.

The legal framework: PTWR requirements

The PTWR were introduced to safeguard part-time workers from discrimination. The PTWR prohibit treating part-time workers less favourably than comparable full-time workers with respect to terms of employment or any other detriment, unless this can be objectively justified.

Under the PTWR, a claimant must establish that:

1. They are a part-time worker
2. They were treated less favourably than a comparable full-time worker
3. The less favourable treatment was because they worked part-time — and not for any other reason

The case of Mireku centres primarily on the third element.

Case background: Mireku v London Underground Ltd

Mr Mireku, a part-time Customer Service Supervisor (CSS) at London Underground, brought a claim under the PTWR. He alleged that he was treated less favourably than comparable full-time workers in relation to the cancellation of an overtime request.

An employment tribunal rejected his claim, finding that the overtime was cancelled for operational reasons not connected to his part-time status. Mr Mireku appealed, arguing that the tribunal had applied the wrong causation test.

EAT decision: part-time status must be the sole cause

The EAT dismissed Mr Mireku’s appeal.

The EAT acknowledged that there were conflicting authorities on the question of causation under the PTWR and reviewed previous cases. It held that, for a claimant to be successful, part-time status must be the sole cause of less favourable treatment and that, whilst Mr Mireku may have received fewer opportunities, his part-time status was not the sole reason for this. Instead, the EAT held that the cancellation of overtime was due to staff confusion.

Learning points for employers

• If employers can demonstrate a legitimate, alternative reason for a policy or action (e.g., operational efficiency or availability requirements), this may defeat a PTWR claim.
• The tribunals will look for clear causal evidence linking part-time status to the treatment complained of.
• Employers must ensure that processes affecting workers (e.g. training, promotion, workload allocation) are based on objective, role-related criteria — not working patterns alone.
• An employer can defend a claim based on less favourable treatment, if the employer can justify the treatment if it aims to achieve a legitimate objective and if it is a necessary and appropriate way of achieving that objective.
• Where business or operational needs lead to differences in treatment, document these clearly and contemporaneously. For example, if training is scheduled only during full days, note this in your rationale to show that exclusion of part-time staff was incidental and not discriminatory.

Comment

The Mireku v London Underground Ltd case is a key authority for employers navigating part-time worker claims. It reinforces that only differential treatment solely caused by part-time status will breach the PTWR.

For employers, this ruling provides greater clarity and protection — but also a reminder to back up decisions and policies with clear, fair, and non-discriminatory reasoning.