4Where a structure plan is in force in any district, but no local plan is in force in that district, a street authorisation map prepared in pursuance of the [S.I. 1965/1453.] Town and Country Planning (Development Plans) Regulations 1965 or the [S.I. 1966/48.] Town and Country Planning (Development Plans for Greater London) Regulations 1966 for any area consisting of or comprising that district shall—
(a)if in force immediately before the structure plan comes into force be treated for the purposes of this Act as having been adopted as a local plan by the local planning authority ;
(b)if immediately before the structure plan comes into force it was under consideration by the Secretary of State be treated for those purposes as having been so adopted on being approved by the Secretary of State.