Regulation 4 Variation and revocation of exemption certificates
If it appears to the Secretary of State that there has been a material change in the circumstances of a combined heat and power station such that—
it no longer satisfies the prescribed conditions as being fully exempt; or
in the case of a partly exempt station, it now satisfies the prescribed conditions as being fully exempt; or
its efficiency percentage has fallen below, or, as the case may be, risen to equal or exceed the threshold efficiency percentage,
he shall vary its exemption certificate by revising the particulars mentioned in regulation 3(4)(c) or (d), as appropriate.
If—
a combined heat and power station ceases to operate;
the operator fails to comply with regulation 3(2); or
the operator makes a written request to that effect to the Secretary of State,
the Secretary of State shall revoke the exemption certificate.