Parker v Chief Constable of Essex Police  EWHC 2140 (QB),  MHLO 27
"The Defendant founds its submission that the Claimant is entitled to nominal damages only on the decision of the Supreme Court in Lumba (WL) v SSHD  UKSC 12. Lumba has been considered and applied by the Supreme Court in R (Kambadzi) v SSHD and by the Court of Appeal in Bostridge v Oxleas NHS Foundation Trust  EWCA Civ 79,  MHLO 12. The Defendant relies upon Kambadzi and Bostridge as well as Lumba. ... Applying the basic principles of compensatory damages in tort, the counterfactual (i.e. what would have happened if the tort had not been committed) in Lumba was that the Secretary of State would have detained the claimants lawfully pursuant to the published policy. ... In Bostridge the finding of the trial judge was that the appellant would have been detained as and when he was if his illness had been correctly addressed via section 3 of the Mental Health Act, as it should have been; and that he would then have received precisely the same treatment and been discharged when he was. The Court of Appeal held that the fact that this counterfactual necessarily included steps being taken by persons other than the Defendant did not prevent the application of the principles set out in Lumba. The appellant therefore recovered only nominal damages. It is not enough for a Defendant in the position of the Secretary of State in Lumba or the Defendant in the present case to show that the counterfactual could have resulted in the same outcome as had been caused by the tort: the Defendant must go on to show that it would have done so. ... It follows that I reject the Defendant's submission that the principles set out in Lumba are applicable if the unlawfully arrested Claimant was "arrestable", meaning that he could have been lawfully arrested: it is necessary for the Defendant also to show that he would have been lawfully arrested. The principles set out in Lumba lead to an award of nominal damages if no loss has been suffered because the results of the counterfactual are the same as the events that happened. If and to the extent that they diverge (e.g. because a lawful arrest would not have occurred at the time but would have occurred later) the Court will have to decide on normal tortious compensatory principles whether and to what extent a substantial award of damages is merited for the divergence in outcome. What is the appropriate counterfactual in a given case will be acutely fact-sensitive."
This case has been categorised with unlawful detention cases (e.g. Lumba and Bostridge), even though it relates to the tort of unlawful arrest, because it also considers the principles of compensatory damages in tort.