The appropriate authority may by order made by statutory instrument provide that section 87A(1) above is to have effect as if for "one milligram per litre" there were substituted a lower concentration specified in the order.
An order under subsection (1) above may make different provision for different geographical areas, or for some such areas and not others.
A statutory instrument containing an order under subsection (1) above shall not be made by the Secretary of State (or by the Secretary of State and the Assembly acting jointly) unless a draft of the instrument has been laid before, and approved by a resolution of, each House of Parliament.
In subsection (1) above "appropriate authority"—
An order amending or revoking an order under subsection (1) above made by virtue of subsection (4)(a) above must also be made by the Secretary of State and the Assembly acting jointly.