4.—(1) The person conducting an auction—
(a)may require an account holder to pay a deposit into a nominated bank account on account of payment for allowances,
(b)may retain a deposit as payment for allowances allocated, and
(c)must repay to an account holder any part of a deposit not used to satisfy payment for allowances as soon as reasonably practicable after the close of the bidding window.
(2) In paragraph (1) “bidding window” means such period as is specified in the Scheme during which an account holder may submit a bid in an auction for the allocation of an allowance.