(1)Where a shop worker or betting worker gives his employer an opting-out notice, the contract of employment under which he was employed immediately before he gave that notice becomes unenforceable to the extent that it—
(a)requires the shop worker to do shop work, or the betting worker to do betting work, on Sunday after the end of the notice period, or
(b)requires the employer to provide the shop worker with shop work, or the betting worker with betting work, on Sunday after the end of that period.
(2)Subject to subsection (3), any agreement entered into between an opted-out shop worker, or an opted-out betting worker, and his employer is unenforceable to the extent that it—
(a)requires the shop worker to do shop work, or the betting worker to do betting work, on Sunday after the end of the notice period, or
(b)requires the employer to provide the shop worker with shop work, or the betting worker with betting work, on Sunday after the end of that period.
(3)Where, after giving an opting-in notice, an opted-out shop worker or an opted-out betting worker expressly agrees with his employer to do shop work or betting work on Sunday or on a particular Sunday (and so ceases to be opted-out), his contract of employment shall be taken to be varied to the extent necessary to give effect to the terms of the agreement.
(4)The reference in subsection (2) to an opted-out shop worker, or an opted-out betting worker, includes a reference to an employee who although not an opted-out shop worker, or an opted-out betting worker, at the time when the agreement is entered into—
(a)had given her employer an opting-out notice before that time, and
(b)is an opted-out shop worker, or an opted-out betting worker, on the day on which she returns to work in accordance with section 79, or in pursuance of an offer made in the circumstances described in section 96(3), after a period of absence from work occasioned wholly or partly by pregnancy or childbirth.
(5)For the purposes of section 41(1)(b), the appropriate date—
(a)in relation to subsections (2) and (3) of this section, is the day on which the agreement is entered into, and
(b)in relation to subsection (4) of this section, is the day on which the employee returns to work.