The Treasury may issue to the Secretary of State out of the National Loans Fund such sums as are required by him for making loans under section 66.
The aggregate at any time outstanding in respect of the principal of sums borrowed under section 66(1) shall not exceed £1,834.303 million.
The Secretary of State may by order made with the consent of the Treasury substitute for the amount (or substituted amount) specified in subsection (2) such ... amount as may be specified in the order.
An amount substituted under subsection (3) may be more or less than the amount for which it is substituted but may not be less than £1.75 billion.
Sums received by the Secretary of State under section 66(3) shall be paid into the National Loans Fund.