Essay Answer

You should break down the answer to this question in the following way.

Definitions of the Royal Prerogative

Here you should present and explain the definitions of Royal Prerogative given by Blackburn and Dicey.

Nature and extent of the Royal Prerogative

In this part of your answer you should explain the areas of government covered by Royal Prerogative distinguishing between the personal powers of the monarch and those powers exercised on behalf of the Crown by the Government.

Royal Prerogative and the courts

You should begin this part of your answer by referring back to Dicey's definition of the Royal Prerogative where he says that Royal Prerogative is arbitrary and discretionary. This implies that, apart from a limited right to compensation, Royal Prerogative is beyond judicial control.
Then go on to look at justiciability. Explain Lord Denning's views in the Laker Airways case and then go on to give an in depth account of the justiciability principle in the GCHQ case. This is the heart of the topic and you should spend the most time on this when preparing your answer.

The last part of your answer should be a discussion focusing on the extent to which GCHQ widened the jurisdiction of the court. Back up your answer with relevant case law.