477. Apportionment of liability under covenants binding both assignor and assignee of tenancy or reversion.

The following provisions apply where:

  1.  

    (1)     a tenant1 assigns part only of the premises demised to him by a tenancy2;

  2.  

    (2)     after the assignment3, both the tenant and his assignee are to be bound by a non-attributable tenant covenant of the tenancy4; and

  3.  

    (3)     the tenant and his assignee agree that as from the assignment liability under the covenant is to be apportioned between them in such manner as is specified in the agreement5;

and also apply where:

  1.  

    (a)     a landlord6 assigns the reversion7 in part only of the premises of which he is the landlord under a tenancy8;

  2.  

    (b)