The Part-Time Workers (Prevention of Less Favourable Treatment) Regulations 2000 (PTWR) established a minimum standard of fairness for part-timers so that they cannot be treated less favourably than comparable full-time co-workers, unless the treatment is justified on objective grounds. A comparable full-time worker must work in the same establishment as the part-timer, be engaged in broadly similar work and work under the same type of contract.

In Carl v University of Sheffield, the Employment Appeal Tribunal (EAT) considered the following questions:

• Can a claimant rely on a hypothetical comparator when making a claim under the PTWR?
• Must the worker’s part-time status be the sole reason for the less favourable treatment complained of?

Mrs Carl was a part-time teacher in the Journalism Department at Sheffield University. She complained that she had been treated less favourably than a named comparator, Ms McClelland, who was a full-time teacher in the Sociological Studies Department, or than a hypothetical comparator, should the Employment Tribunal (ET) decide that Ms McClelland was not a true comparator.

In the event, the ET did decide that Ms McClelland was not a true comparator. She had more academic qualifications and her role was quite different from that of Mrs Carl. Her contribution was both vocational and academic, whereas Mrs Carl’s teaching was purely vocational. The ET did, however, accept the hypothetical comparator. It dismissed Mrs Carl’s claim, however, because in its view Regulation 5(2) of the PTWR, which provides that the right to no less favourable treatment applies only if the treatment ‘is on the ground that the worker is a part-time worker’ should be taken to mean solely because they are part time, in order to reflect the wording of the European Directive which the PTWR implement in UK law.

Sheffield University appealed against the decision that a person making a claim under the PTWR can rely on a hypothetical comparator and Mrs Carl appealed against the finding that a claimant must show that the treatment was solely on the ground of her part-time status.

The EAT held that when a claim is made under the PTWR, comparison must be made with an actual full-time worker, not a hypothetical comparator. It then went on to consider conflicting authorities regarding whether or not it is necessary for part-time status to be the sole ground for the less favourable treatment and judged that it need not. In the EAT’s view, part-time work must be the effective and predominant cause of the less favourable treatment complained of but it need not be the only cause.

The EAT also found that the ET had been entitled to conclude that there was no true comparison between the jobs of Mrs Carl and Ms McClelland.