21.—(1) The undertaker may acquire compulsorily so much of the Order land described in the book of reference and shown on the land plans as is required for the authorised development or is incidental to it or required to facilitate it.
(2) This article is subject to—
(a)article 23 (compulsory acquisition of rights and restrictive covenants);
(b)article 24 (time limit for exercise of authority to acquire land compulsorily; and
(c)article 30 (temporary use of land for carrying out the authorised development.
(3) Nothing in this article authorises the acquisition of an interest which is for the time being held by or on behalf of the Crown.