The question was whether the court would interfere with the orders of Immigration officers to deport two apparently illegal entrants under the Immigration Act. HL said that a reviewing had a duty to inquire whether there had been sufficient evidence to justify the immigration officer's belief that the entry had been illegal and that the duty of the court was not limited to inquiring merely whether there was some evidence on which the immigration officer had been entitled to decide as he had. In judicial review, the home office had to prove on balance of probabilities that Ps were illegal entrants.
Lord Bridge: If an assessment of the facts and their application to the state of affairs were not subjected to rigorous judicial review, then under this statute the immigration officer could detain and deport a person without their having any prospect of a trial to establish whether or not they actually are illegal. Only under the plainest statutory language would a court allow the executive to imprison someone without trial.
Doesn’t answer the question, regarding whether the statutory criteria have been fulfilled, of when deference should be shown or when a more rigorous approach should be used. Hare, in “The Golden Metwand and the Crooked Cord”, argues that deference should only be granted in accordance with constitutional principle e.g. if the exec has specialist knowledge in an area.
Alternatively, maybe we could look to statutory construction and parliamentary intention (i.e. if the criteria are vague then parl must have intended DM to have a wide discretion)