Where a development gain accrues to a person in respect of a disposal of an interest in land to which section 38 of this Act applies, being a disposal in relation to which section [sections 115 to 121 of the Capital Gains Tax Act 1979 F2] (replacement of business assets) [apply F2], then, if a claim under [those sectionsF2] is made as respects the whole or any part of the consideration for the disposal, the consideration obtained by him for the disposal shall be treated for the purposes of [those sections in their applicationF2] in relation to the disposal as if it were equal to the amount by which the actual consideration obtained by him exceeds the amount of the said development gain.