Workers are protected against being subjected to a detriment if the sole or main purpose of an employer's act (or failure to act) is to prevent or deter them from taking part in the activities of an independent trade union. In Bone v North Essex Partnership NHS Trust the Court of Appeal had to examine that right in the context of a dispute between a recognised and a non-recognised trade union.

The claimant employee was an active member of (or, as the Court of Appeal put it "the leading light" in) the Workers of England Union (WEU). This was a small independent trade union that was not recognised by the employer, which already recognised a number of trade unions in the workplace, including Unison. The evidence before the employment tribunal indicated that officials of Unison who were also employees of North Essex Partnership NHS Trust had conducted a campaign of bullying and harassment against the claimant because of his active participation in the WEU. Although the employer had not participated in the campaign, it had not taken effective steps to investigate the conduct or to suspend or discipline the employees responsible. This amounted to a detriment and it was reasonably foreseeable that this would deter the claimant from taking part in the activities of his trade union at an appropriate time.

In the Court of Appeal the employer argued that its sole or main purpose in failing to investigate or deal with the campaign against the claimant was its desire to maintain neutrality between Unison and the WEU. Its purpose could not therefore be to deter the claimant from taking part in the WEU's activities. It was not sufficient that this was the effect of its failure to act.

The Court of Appeal rejected that argument. The tribunal had found that the main purpose of the employer's failure to act was to eliminate or marginalise the effect of the WEU at the workplace, that the employer was well aware that this might be the consequence of inaction and that their motivation was to placate Unison. It had not accepted that the employer's purpose was simply to maintain its neutrality between the two unions. The tribunal was entitled to reach the decision it had and to conclude that the employer's failure to take effective steps to protect the claimant from the campaign against him was a breach of his rights.