6.—(1) Subject to paragraph (2), these Regulations do not apply to a silo, slurry storage system or fuel storage tank—
(a)which, before 1 March 1991, was being used for the purpose of making silage, storing slurry or, as the case may be, storing fuel oil;
(b)where it was not used before 1 March 1991 for that purpose, it was constructed before that date for such use; or
(c)in relation to which—
(i)a contract for its construction, substantial enlargement or substantial reconstruction was entered into before 1 March 1991, or
(ii)such work was commenced before that date, and
and in either case the work was completed before 1 September 1991.
(2) These Regulations apply to a silo, slurry storage system or fuel storage tank meeting the requirements of paragraph (1) if any requirement of a notice under regulation 7 is not complied with within the period stated in the notice.
(3) Any reference in paragraph (2) to the period stated in a notice is to that period as extended if it has been extended under regulation 7(6)(b) or by virtue of regulation 8(6) and any reference in those paragraphs to a requirement of a notice is to that requirement as modified if it has been modified under regulation 7(6).