(1) Where protected information has come into the possession of an authorised officer by virtue of an interception direction or an entry warrant or both, under this Act, or by means of the exercise of a statutory power to seize, detain, inspect, search or otherwise to interfere with documents or other property, or is likely to do so, or has otherwise come into possession of an authorised officer by any other lawful means, and he or she has reasonable grounds to believe that—
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(a) a key to the protected information is in the possession of any person; and
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(b) disclosure of the information is necessary for any of the purposes specified in section 5(1)(a)(i) or (ii);