In certain subject matters identified by common law, courts can legally supervise the Crown use of the royal prerogative in the same way that they review the manner in which statutory powers are exercised.
Council of Civil Service Unions v Minister for the Civil Service (1985) 1 AC 374 (the GCHQ case) or (the CCSU case).
The Prime Minister issued an instruction that civil servants would no longer be permitted to be members of trade unions without previously consulting civil servants already members of trade unions. Civil servants sought judicial review of the said instruction for breach of the duty to act fairly. The government justified the lack of consultation by national security considerations.
In the GCHQ case the House of Lords upheld that the mere fact that the instruction was derived from royal prerogative does not justify immunity for government actions from the courts’ jurisdiction. As Lord Roskill stated:
“I am unable to see (…) that there is any logical reason why the fact that the source of the power is the prerogative and not statute should today deprive the citizen of that right of challenge to the manner of its exercise which he would possess were the source of the power statutory. In either case the act in question is the act of the executive”.
However, The House of Lords held that it was for the executive and not for the judiciary to decide whether or not consulting the civil servants because of national security considerations.
In this case, the House of Lords expressly stated that the manner in which common law powers, as any other statutory powers, are exercised by the executive, were subject to supervision of the courts. In other words, by adopting this decision, the House of Lords removed any doubts about the fact that prerogative powers were covered by judicial review, resulting on a subsequent practice of control of the Crown’s use of the prerogative by the courts.
According to the House of Lords (HL), both prerogative and executive action derived from legislation had to adhere to rules of judicial review (Lord Diplock) and were justiciable. This would normally imply that procedural propriety had to apply, which would indicate that the union would prevail in a typical scenario. However, in the case of matters pertaining to national security, an exception was established (the High Court stating that matters pertaining to national security are a matter that should be judged exclusively by the executive, due to the fact that some evidence could compromise security if shown in a public court), and as a result, the judicial review rule of "procedural propriety" was not applicable. The issue of national security was one that Lord Scarman underlined in particular. In the past, the scope of judicial review was limited to determining whether or not a prerogative existed and, if so, what its boundaries were. In this particular instance, HL contended that it had the authority to scrutinise the process that was used to exercise a prerogative.