Look at whether the defendant himself believed force was necessary
objective test
whether force used was reasonable
definition s3 (1) criminal law act
"A person may use such force as is reasonable in the circumstances or in affecting or assisting in the lawful arrest of offenders or suspected offenders, or if persons unlawfully at large"
key case
R(bennet) v HM Coroner
Bennett shot by police officer after report he was carrying a gun.
