5.—(1) Where the whole or part of a hereditament or agricultural unit is comprised in land of any of the specified descriptions and a person claims that—
(a)he is entitled to an interest in that hereditament or agricultural unit which qualifies for protection under this Order, and
(b)he has made reasonable endeavour to sell that interest, and
(c)in consequence of the fact that the hereditament or unit or part of it was, or was likely to be, comprised in land of any of the specified descriptions, he has been unable to sell that interest except at a price substantially lower than that for which it might reasonably have been expected to sell if no part of the hereditament or unit were, or were likely to be, comprised in such land,
he may serve on the appropriate authority a blight notice in the prescribed form requiring that authority to purchase that interest to the extent specified in, and otherwise in accordance with, this Order.
(2) Paragraph (1) applies to an interest in part of a hereditament or agricultural unit, but this paragraph does not enable any person—
(a)if he is entitled to an interest in the entirety of a hereditament or agricultural unit to make any claim or serve a blight notice in respect of his interest in part of the hereditament or agricultural unit; or
(b)if he is entitled to an interest only in part of a hereditament or agricultural unit, to make any claim or serve a blight notice in respect of his interests in less than the entirety of that part.