The enforcing authority may at any time, subject to the requirements of section 7 above, and, in cases to which they apply, the requirements of Part II of Schedule 1 to this Act, vary an authorisation and shall do so if it appears to the authority at that time that that section requires conditions to be included which are different from the subsisting conditions.
Where the enforcing authority has decided to vary an authorisation under subsection (1) above the authority shall notify the holder of the authorisation and serve a variation notice on him.
In this Part a "variation notice" is a notice served by the enforcing authority on the holder of an authorisation—
and, unless the notice is withdrawn or is varied under subsection (3A) below, the variations specified in a variation notice shall take effect on the date or dates so specified.
An enforcing authority which has served a variation notice may vary that notice by serving on the holder of the authorisation in question a further notice—
and any reference in this Part to a variation notice, or to a variation notice served under subsection (2) above, includes a reference to such a notice as varied by a further notice served under this subsection.
A variation notice served under subsection (2) above shall also—
Where in the opinion of the enforcing authority any action to be taken by the holder of an authorisation in consequence of a variation notice served under subsection (2) above will involve a substantial change in the manner in which the process is being carried on, the enforcing authority shall notify the holder of its opinion.
The Secretary of State may, if he thinks fit in relation to authorisations of any description or particular authorisations, direct the enforcing authorities—
and the Secretary of State shall have the corresponding power of direction in respect of the powers of the enforcing authorities to vary authorisations under section 11 below.
In this section and section 11 below a "substantial change", in relation to a prescribed process being carried on under an authorisation, means a substantial change in the substances released from the process or in the amount or any other characteristic of any substance so released; and the Secretary of State may give directions to the enforcing authorities as to what does or does not constitute a substantial change in relation to processes generally, any description of process or any particular process.
In this section and section 11 below—
"prescribed" means prescribed in regulations made by the Secretary of State;
"vary" and "variation" shall be construed accordingly.
(a), in relation to the subsisting conditions or other provisions of an authorisation, means adding to them or varying or rescinding any of them; and
(b)in relation to a variation notice, means adding to, or varying or rescinding the notice or any of its contents;