Where an interest in land is acquired in pursuance of a blight notice and the interest is one—
(a) in respect of which a compulsory purchase order is in force under section 1 of the Act of 1946 (as applied by section 50 of this Act) containing a direction for minimum compensation under section 53 of this Act; or
(b) in respect of which a compulsory purchase order is in force under Part III of the Housing Act 1957,
the compensation payable for the acquisition shall, in a case falling within paragraph (a) above, be assessed in accordance with the direction mentioned in that paragraph and, in a case falling within paragraph (b) above, be assessed in accordance with Part III of the said Act of 1957, in either case as if the notice to treat deemed to have been served in respect of the interest under section 142 of the principal Act had been served in pursuance of the compulsory purchase order.