Necessity

• Def acted to prevent greater evil from happening
• (Re A - conjoined twins) sets out test for necessity
• 1. act was necessary to avoid inevitable evil
  2. no more evil than necessary was done
  3. evil inflicted was not disproportionate to evil avoided
• Not defence to murder (Dudley and Stephens)
• Can be used to sterilise those with severe mental disability without consent (Re F)
• Cant be used for cannabis (R V Quayle)