"Since arrest involves trespass to the person and any trespass to the person is prima facie tortious, the onus lies on the arrestor to justify the trespass by establishing reasonable and probable cause for the arrest. ... One word about the requirement that the arrestor... should act honestly as well as reasonably. In this context it means no more than that he himself at the time believed that there was reasonable and probable cause, in the sense that I have defined it above, for the arrest... The test whether there was reasonable or probable cause for the arrest... is an objective one, namely whether a reasonable man, assumed to know the law and possessed of the information which in fact was possessed by the defendant, would believe that there was reasonable and probable cause. Where that test is satisfied, the onus lies on the person who has been arrested ... to establish that his arrestor ... did not in fact believe what ex hypothesi he would have believed had he been reasonable. ... In the nature of things this issue can seldom seriously arise. Next, as to procedure. In arresting [or] detaining... a suspected felon, a person is acting in furtherance of the administration of justice. It is a well-settled rule of procedure that the question whether he is acting reasonable is one to be decided by the judge. It may be that this rule reflects the judicial distrust of Jacobinism among juries at the formative period of this branch of English law; but it can at least be rationalised on the ground that the judge, by reason of his office and his experience, is better qualified that a juryman to determine what conduct is reasonable or unreasonable in furtherance of the administration of justice. In those days, however, the jury was the only tribunal which at common law was competent to determine disputed issues of fact. If there was conflicting evidence as to what had happened, that is what the conduct of the defendant in fact was, the jury alone was competent to resolve the conflict. But when what had happened was established whether by uncontradicted evidence or, in the case of conflict, by the jury's finding of fact, it was for the judge to rule whether the defendant's conduct was reasonable or unreasonable. This is still the position today where an action for false imprisonment... arising out of the arrest [or] detention... of a suspected felon is tried by judge and jury. It is for the judge to decide what facts given in evidence are relevant to the question of whether the defendant acted reasonably. It is thus for him to decide, in the event of a conflict of evidence, what finding of fact is relevant and requisite to enable him to decide that question. A jury, however, is entitled to base findings of fact only on the evidence called before it, and, as in any other jury trial, it is for the judge in an action for false imprisonment, to decide whether the evidence on a relevant matter does raise any issue of fact to fit be left to the jury. If there is no real conflict of evidence, there is no issue of fact calling for determination by the jury. This applies not only to the issues of fact as to what happened on which the judge has to base his determination whether the defendant acted reasonably, but also to the issue of fact whether the defendant acted honestly, which, if there is sufficient evidence to raise this issue, is one for the jury (see Herniman -v- Smith ). For the reasons already indicated, however, where there is reasonable and probable cause for an arrest ... the judge should not leave this to the jury except in the highly unlikely event that there is cogent positive evidence that despite the actual existence of reasonable and probable cause, the defendant himself did not believe that it existed (see Glinski -v- McIver )."
"In my judgment the evidence does not support that proposition"