Section 18 of the Offences Against the Person Act 1861 states that:

Whosoever shall unlawfully and maliciously by any means whatsoever wound or cause any grievous bodily harm to any person, with intent to do some grievous bodily harm to any person, or with intent to resist or prevent the lawful apprehension or detainer of any person, shall be guilty of an offence triable only on indictment, and being convicted thereof shall be liable to imprisonment for life.

Actus reus

The actus reus for s.18 is similar to s.20 and requires proof of either GBH or wounding. The actus reus of wounding and the actus reus of GBH have the same meaning as under s.20.

Mens rea (Latin for a guilty mind, or criminal intent in committing the act)

To Satisfy the mens rea, the prosecution must prove intention to cause GBH or intention to avoid arrest. The crucial difference between s.20 and s.18GBH is in the mens rea; while recklessness can be sufficient for s.20, intention is always required for s.18.