Within any one district there shall, as far as is reasonably practicable having regard to paragraph 17, be substantially the same number of local electors in each ward.

For the purposes of sub-paragraph (1) it shall be taken that the electors in each ward are the persons registered as local electors, by virtue of a qualifying address within that ward, in the register of electors last published before the making of the announcement mentioned in paragraph 6(2), 7(2) or 8(2) (as the case may be).