Paragraph 5 of Schedule 8 to the [1973 c. 51.] Finance Act 1973 and paragraph 18 of Schedule 10 to the Finance Act 1980 (certain matters deemed to be restrictions attaching to shares) shall each have effect and shall be deemed always to have had effect as if the references in those paragraphs to any contract, agreement, arrangement or condition did not include a reference to so much of any contract, agreement, arrangement or condition as contains provisions similar in purpose and effect to any of the provisions of the Model Rules set out in the Model Code for Securities Transactions by Directors of Listed Companies issued by the Stock Exchange in April 1981.