Sch 2 para 9
(1) The witness cannot be compelled to give any evidence which he could not be compelled to give in criminal proceedings in the part of the United Kingdom in which the nominated court exercises jurisdiction. (2) The witness cannot be compelled to give any evidence if his doing so would be prejudicial to the security of the United Kingdom. (3) A certificate signed by or on behalf of the Secretary of State or, where the court is in Scotland, the Lord Advocate to the effect that it would be so prejudicial for that person to do so is to be conclusive evidence of that fact. (4) The witness cannot be compelled to give any evidence in his capacity as an officer or servant of the Crown. (5) Sub-paragraphs (2) and (4) are without prejudice to the generality of sub-paragraph (1).