1Where a rent for a dwelling-house which is subject to a regulated tenancy is registered under Part IV of the Act of 1971 and the registration is the first registration to take effect after the tenancy has become a regulated tenancy by virtue of section 34 of this Act, then if the rent payable under the tenancy for any statutory period beginning during the period of delay imposed by paragraph 2 of this Schedule is less than the rent so registered, it shall not be increased by a notice of increase under section 21(2)(b) of the Act of 1971 except to the extent (if any) permitted under the following provisions of this Schedule ; and any such notice which purports to increase it further shall have effect to increase it to the extent so permitted but no further.