The claimant in Unite the Union v Nailard was employed by the trade union as a regional officer at their office at Heathrow. Her managers were two other paid union employees. There were also two elected full-time union officials at Heathrow, both employed by the airport. They bullied and harassed the claimant (mostly at meetings); this amounted to sexual harassment under the Equality Act.

The Employment Tribunal found that the union was vicariously liable for this unlawful conduct, on the basis that the elected officials were either union employees or they were acting as its agents. The EAT decided that the Tribunal had been wrong about them being union employees – there was no contract to work personally for the union – but that they were agents. They were acting within the scope of their authority as union officers in their interactions with the claimant. The union argued that they weren’t responsible because the officials were acting contrary to union policy. The EAT dismissed this – the union couldn’t avoid responsibility merely by, in effect, saying "you mustn't discriminate unlawfully". Clearly the union wouldn’t have approved of their behaviour, but that didn’t prevent their actions being treated as the union's.

The Tribunal also found that the claimant's managers discriminated against the claimant, by failing to take action against the elected officers to prevent the harassment and by deciding to transfer her elsewhere. Here the EAT decided that the Tribunal had not used the correct test. The question was whether the managers' conduct was “related to sex”; and this test was not met merely because the earlier harassment by the officers was clearly related to sex.

The Tribunal should have focused on the mental processes and motivation of each manager and asked whether their conduct was because of sex. It couldn’t just be assumed that their actions were sex-related. The case was sent back to the Tribunal to revisit the question of motivation.

As the elected officials were found to be the unions' agents, this was not strictly a case about "third party harassment". However, now that the specific provision making employers potentially liable for harassment of employees by third parties has been removed from the Equality Act, the same principles would apply to a scenario where an employee claims that their employer has not done enough to prevent third party harassment.