A person may use such force as is reasonable in the circumstances for the purposes of (in the alternative): -

In assessing the reasonableness of the force used, prosecutors should ask two questions:

The courts have indicated that both questions are to be answered on the basis of the facts as the accused honestly believed them to be (R v Williams (G) 78 Cr App R 276), (R. v Oatbridge, 94 Cr App R 367).

To that extent, it is a subjective test. There is, however, an objective element to the test. The jury must then go on to ask themselves whether, on the basis of the facts as the accused believed them to be, a reasonable person would regard the force used as reasonable or excessive.

It is important to bear in mind when assessing whether the force used was reasonable the words of Lord Morris in (Palmer v R 1971 AC 814);

"If there has been an attack so that self-defense is reasonably necessary, it will be recognised that a person defending himself cannot weigh to a nicety the exact measure of his defensive action. If the jury thought that in a moment of unexpected anguish a person attacked had only done what he honestly and instinctively thought necessary, that would be the most potent evidence that only reasonable defensive action had been taken ..."

The fact that an act was considered necessary does not mean that the resulting action was reasonable: (R v Clegg 1995 1 AC 482 HL). Where it is alleged that a person acted to defend himself/herself from violence, the extent to which the action taken was a necessary will, of course, be integral to the reasonableness of the force used.

In (R v O’Grady 85 Cr App R 315), it was held by the Court of Appeal that a defendant was not entitled to rely on, so far as self-defense is concerned, upon a mistake of fact that had been induced by voluntary intoxication.