The following matters may, in the circumstances mentioned in subsection (2) of this section, be referred to a Planning Inquiry Commission, that is to say—
Any of the matters mentioned in subsection (1) of this section may be referred to any such commission under this section if it appears expedient to the responsible Minister or Ministers that the question whether the proposed development should be permitted to be carried out should be the subject of a special inquiry on either or both of the following grounds—
Two or more of the matters mentioned in subsection (1) of this section may be referred to the same commission under this section if it appears to the responsible Minister or Ministers that they relate to proposals to carry out development for similar purposes on different sites.
Where a matter referred to a commission under this section relates to a proposal to carry out development for any purpose at a particular site, the responsible Minister or Ministers may also refer to the commission the question whether development for that purpose should instead be carried out at an alternative site.
The responsible Minister or Ministers shall, on referring a matter to a commission under this section, state in the reference the reasons therefor and may draw the attention of the commission to any points which seem to him or them to be relevant to their inquiry.
A commission inquiring into a matter referred to them under this section shall—
Schedule 10 to this Act shall have effect for the construction of references in this section and in section 49 of this Act to " the responsible Minister or Ministers ".