Until a unitary development plan becomes operative for the area of the Island council (or where parts of such a plan become operative on different dates until every part of such a plan has become operative) Part I of Schedule 2 to the 1990 Act (which provides for existing plans to continue in force) shall apply to that area, and Part III of that Schedule shall apply in relation to it for the purposes of making continuing provision for the transitional matters for which provision was made immediately before the commencement of the 1990 Act by Schedule 7 to the Town and Country Planning Act 197110 (old development plans, etc.).