(1) Where at any time before the 9th day of June, 1952, a tenant has sub-let the whole or any part of the premises and the sub-tenant is, at the commencement of this Act, in occupation of such premises, then, notwithstanding that the consent of the landlord was not obtained for such sub-letting, the premises shall be deemed to have been lawfully sub-let.
     (2) No premises which have been sub-let either in whole or in part on or after the 9th day of June, 1952, without obtaining the consent in writing of the landlord, shall be deemed to have been lawfully sub-let.
     (3) After the commencement of this Act, no tenant shall, without the previous consent in writing of the landlord,--
         (a) sub-let the whole or any part of the premises held by him as a tenant; or
         (b) transfer or assign his rights in the tenancy or in any part thereof.