Part-time worker claims: part-time status must be the “sole reason” for less favourable treatment, EAT confirms

In this article, we look at the recent case of Mireku v London Underground Ltd [2025] EAT 57 and its impact on less favourable treatment claims.

The EAT has followed its previous decision in Augustine v Data Cars Limited [2025] ICR 19 which narrows the scope of claims brought under the Part-Time Workers Regulations 2000.

Part-Time Workers Regulations

The Part-Time Workers Regulations 2000 (the “Regulations”) provide protection to employees and workers who work part-time. Specifically, part-time workers have the right not to be treated less favourably than a comparable full-time worker:

• in the terms of their contract; or

• by being subjected to any other detriment by any act, or deliberate failure to act.

Less favourable treatment “on the ground” that a worker is part-time is prohibited, unless that treatment can be objectively justified.

The Regulations apply to all workers, not just employeesandthere is no qualifying period or upper age limit for bringing a claim. There is also no exemption for small businesses.

Where there is a breach of the Regulations, workers can bring a claim in the Employment Tribunal.  Where a claim is successful, the Tribunal can:

• make a declaration as to the rights of the parties;

• award just and equitable compensation to the worker; and/or

• make a recommendation that the employer take action to address the adverse effect on the worker.

Decision in Mireku

The case concerned Mr Mireku, who was a Customer Service Supervisor for London Underground. Mr Mireku had worked for London Underground since 2005. He was based at Paddington and in January 2022 he signed a job share arrangement to work two weeks 'on' and two weeks 'off'.

Following his change to part-time working, Mr Mireku requested overtime over several months and was unhappy with how his requests for overtime were handled. 

In May 2022 Mr Mireku was initially informed that he could not work overtime during one of his “off weeks” under his job-sharing arrangement, and his scheduled overtime in June was cancelled on this basis. 

When Mr Mireku challenged this restriction on overtime, Stations Resourcing indicated that a person on a job share could work additional hours when they were available.  The Paddington Area Manager took this to mean that Mr Mireku could work overtime during his “off” weeks.

Around September 2022, Mr Mireku moved sites from Paddington to Whitechapel.  However, approval for any overtime remained with the Paddington Area Manager, as overtime was paid to Mr Mireku out of Paddington’s budget.  This led to some confusion about what overtime Mr Mireku was able to work at Whitechapel and when.

A further attempt to clarify the arrangement was made on 11 October and Mr Mireku was told that the Paddington Area Manager was happy to pay for 1 shift per week overtime if there was a business need.

On 19 October 2022, Mr Mireku made a request to work overtime between 22 – 28 October.  Whilst initially informed that he had been pencilled in for overtime on 22 and 25 October, a Customer Service Manager emailed him later the same day to cancel the overtime because it was not his working week. 

In November, Mr Mireku moved again, this time to the Edgware Road and Euston Square areas.  The Paddington Area Manager contacted the new Area Managers to say that he could apply for any overtime advertised, just like any other member of staff, and also agreed to be responsible for the overtime costs.  Unfortunately, Mr Mireku was not included on the mailing list which detailed these overtime vacancies.

Mr Mireku brought a less favourable treatment claim under the Regulations.  His complaints included the refusal of his overtime because he was job sharing and the cancellation and limitation of his overtime. 

The Employment Tribunal rejected his claim. Whilst the initial refusal and cancellation of overtime in May 2022 was less favourable treatment, these complaints were out of time. The Tribunal also dismissed his other complaints, including the cancellation of his overtime in October, as the reason(s) for the less favourable treatment were not connected to his part-time status.

Mr Mireku appealed to the EAT, arguing that the Employment Tribunal had applied the wrong test of causation. Specifically, that “on the ground” in the Regulations meant the “effective and predominant cause” of the treatment was part-time worker status.  It did not necessitate a limited view, such that part-time status had to be the “sole ground” for any less favourable treatment.  

Mr Mireku argued that on this wider interpretation, the Tribunal’s finding that the refusal of his overtime on 19 October was due to confusion and mistake because “staff were not sure how to process it” needed to be revisited, to determine whether any such confusion arose because of his part-time status.

The EAT accepted that there were conflicting cases as to causation. In the case of McMenemy v Capita Business Services Ltd [2007] SC 492, the Court of Session determined that part-time status must be the sole reason for less favourable treatment.  Whereas in Sharma v Manchester City Council [2008] ICR 623 and Carl v University of Sheffield [2009] ICR 1286, the EAT concluded that part-time status was required to be an “effective and predominant cause” of the less favourable treatment.

However, after addressing the Employment Tribunal’s findings, the EAT upheld the decision in Augustine that, for there to be a breach of the Regulations, part-time status must be the sole reason for the less favourable treatment.  As a result, Mr Mireku’s appeal was dismissed.

The EAT acknowledged that therehad been a comprehensive review of earlier cases in Augustine and the EAT in that case had considered itself bound to follow McMenemy. On the specific question of precedent, in the circumstances it was inappropriate for the EAT to depart from Augustine.  Unless and until a higher court took a different approach (and the EAT noted that Augustine had recently been heard in the Court of Appeal, although judgment was reserved), the McMenemy test of causation must be followed.

In any event, the EAT noted that Mr Mireku's claim was bound to fail anyway, as he had not relied upon a comparable full-time worker as his comparator, which was a requirement of the Regulations.

The reserved judgment confirming the outcome of the appeal in Augustine is expected imminently. 

Implications for employers

At first glance, employers may sigh in relief at the findings in the Mireku case, given its effect on limiting the scope of future less favourable treatment claims. 

However, the Mireku case also serves as a reminder to employers to be careful not to inadvertently treat part-time staff less favourably. 

The Department for Business and Trade guidance on part-time workers was archived in 2010 but still remains a useful resource for employers regarding best practice: Part-time workers. The law and best practice - a detailed guide for employers and part-timers - BIS.

Clear and consistent communication is key to maintaining good employee relations and avoiding claims under the Regulations. Whilst Mr Mireku’s claim was ultimately unsuccessful, the Tribunal found that the initial refusal and cancellation of his overtime constituted a breach of the Regulations.  Had communications been clearer with Mr Mireku and with his respective managers about his entitlement to work overtime, the claim may have been avoided.

Audits of part-time worker terms and conditions can prove useful to avoid less favourable treatment. Before looking at putting in place any arrangements which may adversely impact upon part-time workers, employers should consider a risk or other assessment to manage any risks, which may include considering whether there may be any objective justification for any difference in treatment. However the scope for objective justification is in practice, quite limited.

In all cases, keeping a record of any decisions taken in relation to part-time workers will be important to defend potential claims.

If you would like to discuss any aspect of this article further, please contact our employment team on 0113 244 6100. 

You can also keep up to date by following Wrigleys Solicitors on LinkedIn.

The information in this article is necessarily of a general nature. The law stated is correct at the date (stated above) this article was first posted to our website.

Specific advice should be sought for specific situations. If you have any queries or need any legal advice please feel free to contact Wrigleys Solicitors.