Where application is made to the Registrar to register any lease which is not compulsorily registrable under this Act but which is capable of registration, the Registrar shall not register such lease unless—
(a) it is in the prescribed form, or in such form as the Registrar may approve; and
(b) in the case of a sublease, every lease superior to that sublease complies with condition (a) and is registered in priority to the sublease.