Mace Ltd & Ors v Persons Unknown (Rev 1)

Quia timet injunctive relief may be granted against persons unknown where there is a sufficiently real and imminent risk of trespass, and the threatened harm would be grave and irreparable so that damages would be inadequate. The court must define the defendant class and prohibited conduct with particular precision. An injunction should target the specific threatened mischief, rather than prohibit trespass generally or depend on a person’s intention. Interim relief must remain temporary and proportionate, with clear geographical and temporal limits. The potential deterrent effect of an injunction may justify relief even where enforcement could be difficult.

The claimants were a construction company and the owners of a construction site at 40 Leadenhall Street, London. They sought, without notice, quia timet injunctive relief against persons unknown to prevent urban explorers entering the site and climbing its structures. No incursion had yet occurred at the site, although comparable trespasses had occurred at other construction sites and the identities of the likely trespassers could not be established.

The application also sought permission to issue proceedings against persons unknown and alternative service. The central issues were whether the anticipated trespass was sufficiently imminent, whether the threatened harm justified anticipatory relief, and how narrowly the injunction should be framed.

1. Relief granted. The court granted permission to issue the claim against persons unknown, made an interim injunction and ordered alternative service.
2. Quia timet threshold. A claimant seeking anticipatory relief must establish a sufficiently real and imminent risk of a tort, together with harm that would be grave and irreparable. The court found a real, imminent and high probability of trespass. The risk of death or serious injury meant that damages would be inadequate.
3. Persons unknown. Applying the six requirements identified in Boyd v Ineos Upstream Ltd, the court found that the likely trespassers could not be named, effective notice could be given, and the order could be framed clearly with appropriate geographical and temporal limits.
4. Precision and proportionality. The order had to address the particular mischief feared, namely urban explorers scaling the site. A proposed prohibition on all trespass would have been disproportionately wide. The operative restriction therefore prohibited climbing more than 5 metres above street level without the claimants’ consent. The site was identified by its address, plan and verbal description.
5. Interim character and deterrence. The order was limited to a period just short of seven months, with a return date, and was therefore not a de facto final injunction. The court also accepted that an injunction could have a real deterrent effect notwithstanding difficulties of enforcement.