The acquiring authority may agree in writing with the owner of any interest which is to vest in the authority under section 8 that the interest is to vest on a date after the vesting date.
If such an agreement is in force on the vesting date, sections 7 and 8 operate in relation to the interest as if the vesting date were—
the agreed date, or
any date subsequently agreed under subsection (1).
If an interest subject to an agreement under this section entitles the owner to possession of the land concerned, the right to enter upon and take possession of the land given by section 8 does not arise until the interest vests in accordance with this section.