for subsection (1) substitute—

“(1)

It shall be the duty of the planning authority to keep under review the matters which may be expected to affect the development of their district or the planning of its development.”;

for subsection (2) substitute—

“(2)

A planning authority may, if they think fit, institute a fresh survey, examining the matters referred to in subsection (1) above, of the whole or any part of their district, and references in subsection (3) of this section to the district of a planning authority shall be construed as including any part of that district which is the subject of a survey under this subsection.”.