Nothing in this Act shall affect the operation of section 79 of the Food and Drugs Act 1955 (special provisions as to the compensation payable under a local Act where the use of a slaughterhouse is rendered unlawful by the provision of a public slaughterhouse) in relation to any slaughterhouse the use of which was rendered unlawful before 1st January 1974 (the date on which section 5(3) of the Agriculture (Miscellaneous Provisions) Act 1972 came into force).