The term ‘necessary’ will take its colour from its context; in ordinary usage it may mean, at one end of the scale, ‘indispensable’ and at the other ‘useful’ or ‘expedient’.
Lord Griffiths said: ‘What then is meant by the words ‘necessary . . for the prevention of . . crime’ in section 10? I do not think that much light is thrown upon this question by an elaborate discussion of the meaning of the word ‘necessary’. ‘Necessary’ is a word in common usage in everyday speech with which everyone is familiar. Like all words, it will take colour from its context; for example, most people would regard it as ‘necessary’ to do everything possible to prevent a catastrophe but would not regard it as ‘necessary’ to do everything possible to prevent some minor inconvenience. Furthermore, whether a particular measure is necessary, although described as a question of fact for the purpose of section 10, involves the exercise of a judgment upon the established facts. In the exercise of that judgment different people may come to different conclusions on the same facts; for an example of this one has to look no further than Secretary of State for Defence v Guardian Newspapers Ltd. But this cannot be avoided and the task of the judge will not be lightened by substituting for the familiar word ‘necessary’ some other set of words with a similar meaning. I do not myself think that it helps to consider the meaning of ‘necessary’ when used in the narrow context of discovery of documents and then apply it to the very broad considerations that will arise when considering the four heads of public interest identified in section 10. I therefore derive no assistance from the discussion of the word ‘necessary’ in Air Canada v Secretary of State for Trade  2 AC 394.
I doubt if it is possible to go further than to say that ‘necessary’ has a meaning that lies somewhere between ‘indispensable’ on the one hand, and ‘useful’ or ‘expedient’ on the other, and to leave it to the judge to decide towards which end of the scale of meaning he will place it on the facts of any particular case. The nearest paraphrase I can suggest is ‘really needed’.’
 AC 660
Company Securities (Insider Dealing) Act 1985 10
England and Wales
Cited – Air Canada v Secretary of State for Trade HL 1983
The court considered the test to be applied before a document could be ordered to be discovered.
Held: (Majority) Discovery is an exception to the adversarial character of the legal process. It assists both the parties and the court to . .
Cited – AMM v HXW QBD 7-Oct-2010
The claimant had sought and been granted an injunction to prevent the defendant publicising matters which had passed between them and which were he said private.
Held: The jurisdiction to grant such injunctions was now established. Publication . .
Cited – Kelly (A Minor) v British Broadcasting Corporation FD 25-Jul-2000
K, aged 16, had left home to join what was said to be a religious sect. His whereabouts were unknown. He had been made a ward of court and the Official Solicitor was appointed to represent his interests. He had sent messages to say that he was well . .
These lists may be incomplete.
Updated: 11 February 2021; Ref: scu.424975