Really serious physical injury (R v Smith  AC 290). In R v Burstow  1 Cr App R 177 it was conceded that severe depression could amount to serious bodily harm.
Under the Offences Against the Person Act 1861 there are several offences involving grievous bodily harm. It is an offence under section 20, punishable by up to five years' imprisonment, to inflict grievous bodily harm upon anyone with the intention to cause any amount of harm (however slight) or while reckless to the risk of causing any amount of harm. It is an offence under section 18, punishable by a maximum sentence of life imprisonment, to cause grievous bodily harm to anyone with the intention of causing serious injury or of resisting or preventing lawful arrest. It had been thought that there was a distinction between the use of the verbs “inflict” and “cause” but it would now seem that they cover the same activities. If a person intends to cause grievous bodily harm but his victim actually dies, he is guilty of murder, even though he did not intend to kill. The courts have said that judges should not attempt to define grievous bodily harm for the jury, but should leave it to them, in every case, to decide whether the harm caused was really serious. See also wounding with intent.