A joint planning board . . . shall, on being authorised to do so by the Secretary of State, have the same power to acquire land compulsorily as the local authorities to whom section 226 applies have under that section.
Such a board shall have the same power to acquire land by agreement as the local authorities mentioned in subsection (1) of section 227 have under that subsection.
Sections 226(1) and (7), 227, 229, 230, 232, 233 and 235 to 242 apply with the necessary modifications as if any such board were a local authority to which those sections applied.
On being authorised to do so by the Secretary of State such a board shall have, for any purpose for which by virtue of this section they may acquire land compulsorily, the power which section 13 of the Local Government (Miscellaneous Provisions) Act 1976 confers on the local authorities to whom subsection (1) of that section applies to purchase compulsorily rights over land not in existence when their compulsory purchase is authorised, and subsections (2) to (5) of that section shall accordingly apply to the purchase of rights under this subsection as they apply to the purchase of rights under subsection (1) of that section.