100A benefit conferred on the Postmaster General by a provision of a local Act passed in the same session as this Act or a previous session or of an order confirmed by an Act so passed consisting in securing that a power conferred by the Act or order to acquire land compulsorily, to secure compulsorily the creation of an easement or other right over land or to execute works on, under or over land shall not, except with his consent or agreement, be exercisable in relation to land specified or described in that provision shall, as from the appointed day, enure for the benefit of the authority.