"The Secretary of State may make regulations about the alteration by listing officers of valuation lists which have been compiled under this Chapter..."
"The regulations may include provision that no alteration shall be made of a valuation band shown in the list as applicable to any dwelling unless - (a) since the valuation band was first shown in the list as applicable to the dwelling - ... (ii) there has been a material reduction in the value of the dwelling."
"... 'material reduction', in relation to the value of a dwelling, means any reduction which is caused (in whole or in part) by the demolition of any part of the dwelling, any change in the physical state of the dwelling's locality or any adaptation of the dwelling to make it suitable for use by a physically disabled person."
"The ratable value of a non-domestic hereditament ... shall be taken to be an amount equal to the rent at which it is estimated the hereditament might reasonably be expected to let from year to year [on three assumptions."
"Where the ratable value is determined with a view to making an alteration to a list which has been compiled (whether or not it is still in force) the matters mentioned in sub-paragraph (7) below shall be taken to be as they are assumed to be on the [material day]."
"matters affecting the physical state of the locality in which the hereditament is situated or which, though not affecting the physical state of the locality, are nonetheless physically manifest there... "
"(1) Subject to the following paragraphs of this regulation, where a billing authority or an interested person is of the opinion that a list is inaccurate because - (d) since the valuation band was first shown in the list as applicable to the dwelling, one (or more) of the events mentioned in subparagraph (a) of paragraph (1) of regulation 4 has occurred."
"(i) there has been a material increase in the value of the dwelling and a relevant transaction has been subsequently carried out in relation to the whole or any part of it; or (ii) subject to paragraph (2), there has been a material reduction in the value of the dwelling; or (iii) the dwelling has become or ceased to be a composite hereditament for the purposes of Part III of the 1998 Act; or (iv) in the case of a dwelling which continues to be a composite hereditament, there has been an increase or reduction in its domestic use."