(1)The appropriate national authority may prescribe rules with respect to the calculation of numbers of persons for the purposes of—
(a)any provision made by or under this Act which is specified in the rules, or
(b)any order or licence made or granted under this Act of any description which is so specified.
(2)The rules may provide—
(a)for persons under a particular age to be disregarded for the purposes of any such calculation;
(b)for persons under a particular age to be treated as constituting a fraction of a person for the purposes of any such calculation.
(3)The rules may be prescribed by order or regulations.