A development corporation's base amount for a year of account is, subject to any adjustment under subsection (2), the amount calculated for the preceding year under section 422, that is to say, the amount of the housing subsidy payable to the corporation for that year or, if none was payable, nil or a negative amount, as the case may be.
If the Secretary of State is of opinion that particular circumstances require it, he may adjust the base amount for amy year by increasing or decreasing it, either generally or in relation to . . . any particular corporation .