Where consideration other than rent is payable under a secure contract, the amount of consideration may be varied—
(a) by agreement between the landlord and the contract-holder, or
(b) by the landlord in accordance with subsections (2) to (4).
The landlord may give the contract-holder a notice setting out a new amount of consideration to take effect on the date specified in the notice.
The period between the day on which the notice is given to the contract-holder and the specified date may not be less than two months.
Subject to that—
(a) the first notice may specify any date, and
(b) subsequent notices must specify a date which is not less than one year after the last date on which a new amount of consideration took effect.
This section is a fundamental provision which is incorporated as a term of all secure contracts under which consideration other than rent is payable.