++++ Common Customs Tariff - Importation free of import duties - Arrangements for goods returned to the customs territory of the Community - Products excluded from the arrangements - Exhaustive set of rules laid down by the Council - Amendment by the Commission on the basis of its implementing powers in agricultural matters - Not permissible - Provision whereby products previously held in intervention are to be treated as products excluded from the arrangements for returned goods - Illegal ( Council Regulation No 754/76, Art . 2(1 ); Commission Regulation No 1687/76, Art . 13a )