What are the key elements of self-defence under criminal law?

Self-defence is a general and complete defence in criminal law (s3(1) Criminal Law Act 1963). It is a justificatory defence. The self-defence defence justifies what would normally be unlawful under criminal law. Self-defence under English criminal law is a defence that allows you to repel force with force. It is acknowledging that in some circumstances you will be permitted to use force against someone else, in order to repel the force they are using towards you. There are two elements to this defence. It is a twofold test: (1) the use of force must be necessary and (2) the use of force must be reasonable. The first (1) test is assessed subjectively and the second (2) test is assessed objectively. The burden of proof to demonstrate self-defence is upon the defendant.