Duress of circumstances and necessity

Can anyone explain the A01 of duress of circumstances and necessity? As well as the evaluation. I'm finding it difficult to understand the concept.

Duress of circumstances is almost identical to the traditional defence of duress (by threats), so the principles for the latter are relevant. The only difference is that threat comes from a circumstance.

1. The accused must have reasonably believed that the circumstances posed a threat of death or serious harm
AND
2. The accused's will must have been overborne (whilst showing reasonable steadfastness), causing him/her to commit the offence.

Duress by circumstances cannot be pleaded to a charge of murder (and related offences, such as attempt) or treason.

The defence of necessity is a more complicated matter, and is not as well-defined. It is often confused with duress by circumstances, but the rules are different.

Simply put, it is a balancing test. Is the evil inflicted by the commission of the offence less than the evil that would have resulted if the accused had not acted? Because of its potentially wide scope (see for example Southwark London Borough v Williams ), it is only permitted when the facts are truly exceptional. Generally the requirements are as follows:

1. The Act is needed to avoid inevitable and irreparable evil
2. No more should be done than reasonably necessary
3. The evil inflicted by the Act should not be disproportionate to the evil avoided.

Duress of Circumstances v Necessity

It may be useful to quickly outline the major differences between the two defences.

1. Necessity is not limited to a threat of death or serious injury. It is available in other circumstances - see F v West Berkshire Authority where forced sterilization by a hospital was protected by the necessity defence in order to stop a psychiatric patient from becoming pregnant.

2. Necessity can be a defence to murder (see Re A)