Where a crofter acquires the site of the dwelling-house on or pertaining to his croft or any croft land forming part of his croft, then, notwithstanding that it is less than seven years since the term at which the existing rent for the croft first became payable, the Land Court may, on the application of the crofter or his landlord, determine a fair rent for the part of the croft which remains subject to the tenancy of the crofter, and accordingly subsections (3) and (4) of section 5 of the Act of 1955 shall apply for the purposes of such a determination as if the provisos to subsection (3) were omitted; but thereafter the said provisos shall apply to a rent so determined.