During emergencies, particularly during wartime, the courts have often been more reluctant to interfere with the exercise of discretionary power. This is whether the power arises from statute or is pursuant to the exercise of the royal prerogative (see Chapter 7).

In Liversidge v Anderson [1942] AC 206, the Home Secretary was empowered under Reg.18B of the Defence Regulations (issued under the Emergency Powers (Defence) Act 1939) to imprison any person if he had 'reasonable cause to believe' such a person had hostile intentions. Liversidge was detained without trial under this regulation and sued the Home Secretary for false imprisonment, claiming that 'reasonable cause to believe' imputed an objective factual standard.

The majority of the House of Lords disagreed, and accepted the Home Secretary's interpretation of the regulation. They held that there was no objective requirement, enabling him to take this action, as long as his belief was an honest one. Thus the courts could not inquire into the grounds for the detention, unless there was evidence to suggest that the Home Secretary had not acted in good faith.

In the minority was Lord Atkin. Famously accusing the majority of being 'more executive minded than the executive', he concluded that, had Parliament wished to give the Home Secretary unlimited discretion, it would not have qualified the grant of power with the word 'reasonable'. In his view, the word purported the existence of facts or a state of facts; therefore the Home Secretary needed to show some evidence for his justification.

While much criticised at the time, Lord Atkin's approach is much closer to current judicial orthodoxy. Even so, the courts have generally remained more cautious in interfering with the grant of wide discretionary powers in times of war or when national security is in issue. This is often described as an example of 'judicial deference'.