3Where two or more interests, other than excepted interests, subsist in the relevant area, the portion of the unexpended balance of established development value of the relevant area attributable to each respectively of those interests shall be taken to be the following, that is to say—
(a)in the case of the interest of the lessor under any lease, so much, if any, of the reversionary development value of that interest, as remains after the deduction therefrom of the aggregate of—
(i)the reversionary development value of the interest of the person, if any, to whom that lessor stands in the relationship of lessee ; and
(ii)in a case where the restricted value of the first-mentioned interest is a minus quantity, an amount equal to that minus quantity ;
(b)in the case of the interest of the lessee under any lease which is not subject to a sub-lease, so much, if any, of the said balance as remains after the deduction therefrom of the aggregate of—
(i)the reversionary development value of the interest of the lessor under the lease, and
(ii)in a case where the restricted value of the first-mentioned interest is a minus quantity, an amount equal to that minus quantity.