Provided that the Board shall not make use of the land under or appurtenant to any lawfully existing and duly authorized building.

Preference to other sites Preference to other sites. The Board shall, as far as may be, make use of the land under this Chapter belonging to the Government, the Central Government, a local authority, government undertaking or autonomous body in preference to other sites: Provided that the prior approval of the Central Government shall be taken if the land in question belongs to the Central Government