6(1)The regulations may require each participant to have or acquire enough allowances to match the participant's activities in a trading period, subject to any offsetting in accordance with provision made under paragraph 7.U.K.
(2)The regulations—
(a)may permit allowances held by a participant at the end of a trading period in excess of the participant's activities in the period to be used to cover the participant's activities in a later trading period,
(b)may permit allowances allocated to a participant for a trading period to be used to cover the participant's activities in an earlier trading period, and
(c)may in either case provide for such use of allowances to be subject to such conditions and limitations as may be specified in or determined in accordance with the regulations.
(3)The regulations must contain provision for ensuring that allowances used by a participant for the purposes of a trading scheme cannot be used by the participant for any other purpose.
(4)The regulations—
(a)may provide for the expiry of allowances after such period as may be specified in or determined in accordance with the regulations;
(b)may enable allowances to be cancelled by a person by whom they are held instead of being used for the purposes of a trading scheme.