Key takeaways
Part-time status need only contribute
Part-time status must be an effective cause, not sole cause.
Protection extends beyond direct targeting
Neutral policies can discriminate when part-timers suffer disproportionate disadvantage.
Justification now key to employer defence
Claims may succeed more easily unless treatment is objectively justified.
In part-time worker discrimination claims, does the worker’s part-time status have to be the ‘sole cause’ or merely an ‘effective cause’ of any less favourable treatment?
The Supreme Court in Augustine -v- Data Cars Limited recently grappled with this difficult question and held that part-time status need only be an effective cause, not the sole cause of the less favourable treatment.
Scope of part-time worker discrimination
Part-time workers have the right not to be treated less favourably due to their part-time status, and to be offered (on a pro rata basis) the same terms as comparable full-time workers (Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000). Unusually, while this is a direct discrimination claim, there is a potential objective justification defence available to the employer.
Historically, there was conflicting case law on whether part-time status needed be the ‘sole reason’ for any less favourable treatment or merely an effective cause of it. Notably, in McMenemy v Capita Business Services Ltd [2007] IRLR 400, the Inner House of the Scottish Court of Session (CSIH) had held that the part-time worker’s status must be the ‘sole reason’ for any less favourable treatment.
Factual background
Mr Augustine worked part-time as a private hire driver for a taxi firm. He claimed part-time worker discrimination, arguing he was treated less favourably because he was charged a circuit fee of £148 per week for access to the taxi firm’s database and the same flat-fee amount was charged to full-time drivers.
Employment Tribunal decision
The employment tribunal rejected Mr Augustine’s claim that the imposition of the flat-rate fee meant he had been treated less favourably than a full-time comparator. In the alternative, taking account of the CSIH’s decision in McMenemy, the tribunal held that the claim should fail in any event because Mr Augustine was not charged the flat-rate circuit fee solely because he was a part-time worker.
Employment Appeal Tribunal decision
On appeal, the Employment Appeal Tribunal (EAT) held that the tribunal had erred in its approach to the question of less favourable treatment. The tribunal had failed to consider the fact that treating someone the same as a comparator can sometimes amount to less favourable treatment. Applying the pro rata principle, Mr Augustine was either paying a greater proportion of his earnings in fees than his full-time comparator, or he was receiving a lower hourly rate of pay after the deduction of fees. The fact that the employer had not intended to treat him less favourably was irrelevant.
However, the EAT also held that the tribunal could not be criticized for applying the ‘sole reason’ test set out in McMenemy. The EAT strongly disagreed with the McMenemy decision, explaining at length why it preferred a test which simply required part-time status to be an effective and predominant cause of any less favourable treatment. However, the EAT felt bound to follow the McMenemy decision on public policy grounds.
Court of Appeal decision
On appeal, the majority of the Court of Appeal disagreed with the McMenemy decision but ultimately the court felt bound to follow it on public policy grounds, leaving the Supreme Court to be the ultimate arbiter.
Supreme Court decision
The Supreme Court held that a worker’s part-time status does not have to be the ‘sole cause’ of their less favourable treatment, rather it need only be an ‘effective’ cause. To hold otherwise would be inconsistent with the standard approach to questions of causation in discrimination cases and would risk uncertainty and unreasonable outcomes.
Within the Supreme Court’s rationale for reaching this conclusion, it noted (as the EAT had done earlier) that ‘discrimination against part-timers often takes place because of factors associated with part-time status so that limiting the protection to less favourable treatment solely on the ground of part-time work risks excluding many cases where the part-time nature of the work might be the effective, but not the sole, reason for that treatment.’
Therefore, it would be wrong to interpret the legislation by limiting it to situations where part-time status was the ‘sole cause’ of the less favourable treatment because this would mean ‘avoiding protection for treatment which inherently and necessarily disadvantages part-time workers (unless that treatment can be justified).’
The Supreme Court also suggested that ‘the fact that not all part-timers are treated adversely should not mean that those who are [affected] cannot take proceedings for discrimination if being part-time is an effective cause (or reason) for their adverse treatment.’ So, if a rule or provision only acts to the detriment of some but not all part-time workers, those who are impacted can still bring a claim.
Finally, the Supreme Court held that the existence of causes of the less favourable treatment other than part-time status may be relevant to determining whether the treatment is justified, or to the amount of compensation awarded.
Determining whether part-time status is an ‘effective cause’
The Supreme Court gave two imaginary hypothetical examples, which we have adapted slightly to illustrate how the ‘effective cause’ test operates in practice:
Example one: an employer denies a particular benefit to all women over six feet tall. This means that a tall woman who suffers the disadvantage does so for two reasons: her sex and her height. As her height is a factor, her sex is not the ‘sole cause’ of her less favourable treatment. However, she can claim sex discrimination because her sex remains an ‘effective cause’ of why she has been excluded from receipt of the benefit.
Example two: an employer refuses a benefit to part-time workers over six feet tall. This means that, irrespective of their sex, a tall part-time worker will suffer a disadvantage for two reasons: their part-time status and their height. While their part-time status is not the ‘sole cause’, they can claim part-time worker discrimination because it is an ‘effective cause’ of the less favourable treatment. The employer may be able to objectively justify the treatment.
Practical implications for employers
The Supreme Court’s decision in Augustine will make it far easier for part-time workers to succeed in their claims, as they will now only need to establish that their part-time status was an ‘effective cause’ of their less favourable treatment; it need not be the only or sole cause.
Strictly speaking, a part-time worker discrimination claim is one of direct discrimination, with a potential objective justification defence. However, in practical terms, the combination of the pro rata principle and the new ‘effective cause’ test means that provisions that on the face of it apply not just to part-timers but instead to all staff, or to particular groups of staff, may now generate claims that are conceptually similar to indirect discrimination claims. Remember that the flat fee policy Mr Augustine complained about did not mention or take account of his part-time status at all – the same fee applied to all drivers irrespective of how many hours they worked. However, applying the pro rata principle, the EAT held that Mr Augustine was being treated less favourably because he was either paying a greater proportion of his earnings in fees than his full-time comparator, or he was receiving a lower hourly rate of pay after the deduction of the flat fee.
The focus will now therefore be on whether an individual’s part-time status has played any part in the less favourable treatment they have experienced. If it has, and they bring a part-time worker discrimination claim, the key battleground will likely be whether the employer can objectively justify its rule, policy or the way the part-time worker was treated.
Therefore, employers should ask both: ‘does this provision discriminate against part-time workers because of their part-time status?’, and ‘are part-time workers likely to suffer a disadvantage or less favourable outcomes due to this provision?’.
This is a good moment for employers to reflect on the detrimental impact their terms and conditions, polices and informal rules may have on part-time workers, and any objective justification arguments they may have, paying particular attention to the following issues:
Pay arrangements including bonuses, commission, overtime pay, allowances, flat fees or deductions (eg deductions for training costs, accommodation charges, professional membership fees, car parking charges, uniform or equipment purchases).
Entitlement to time off (eg entitlement to paid bank holidays, holiday entitlement or restrictions on when holiday can be taken).
Benefit entitlements (eg entitlement to company sick pay, gym membership, life insurance cover, PHI cover or to a company car).
Working time rules (eg normal working hours, shift patterns, entitlement to paid overtime, core office days or hybrid/home working arrangements).
Augustine v Data Cars Limited [2026] UKSC 30
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