9.—(1) In proceedings under this Act, the opinion of any witness F22[who appears to the court or adjudication officer, as the case may be,] to possess the appropriate qualifications or experience as respects the matter to which his or her evidence relates shall, subject to subsection (2), be admissible in evidence as regards any matter calling for expertise or special knowledge that is relevant to the proceedings and, in particular and without prejudice to the generality of the foregoing, the following matters, namely—

(a) the effects that types of agreements, decisions or concerted practices may have, or that specific agreements, decisions or concerted practices have had, on competition in trade,

(b) an F22[explanation to the court or adjudication officer, as the case may be,] of any relevant economic principles or the application of such principles in practice, where such an explanation would be of F22[assistance to the judge, adjudication officer or jury, as the case may be].

(2) Notwithstanding anything contained in subsection (1), F22[a court or adjudication officer, as the case may be, may], where in its opinion the interests of justice require it to so direct in the proceedings concerned, direct that evidence of a general or specific kind referred to in the said subsection shall not be F22[admissible in proceedings under this Act] or shall be admissible in such proceedings for specified purposes only.