Where there were in force immediately before 21st April 1975 arrangements between the Commissioners and any taxable person for supplies made by him (or such supplies made by him as were specified in the arrangements) to be treated as taking place at times or on dates which, had section 6(10) been in force when the arrangements were made, could have been provided for by a direction under that section, he shall be treated for the purposes of that section as having requested the Commissioners to give a direction thereunder to the like effect, and the Commissioners may give a direction (or a general direction applying to cases of any class or description specified in the direction) accordingly.