25.—(1) Subject to paragraph (2), where a house is or has been let by the Executive on a weekly or other periodic tenancy, the Executive, without the tenancy being terminated, may—
(a)substitute a new tenancy agreement for an existing tenancy agreement,
(b)vary the terms of any tenancy agreement,|8by a written notice of substitution or variation given by the Executive to the tenant not less than 4 weeks before the date upon which the substitution or variation is to be made.
(2) A notice of substitution or variation given by the Executive under paragraph (1) shall not be valid unless it tells the tenant of his right to terminate the tenancy and of the steps to be taken by him if he wishes to do so.
(3) In this Article “tenancy agreement” includes every term or condition (other than the amount of rent to be paid) expressed or implied in any contract of letting.
[F1(4) This Article does not apply to a secure tenancy within the meaning of Article 25 of the Housing (Northern Ireland) Order 1983.]