Section 37 — Contractual requirements relating to Sunday work.

(1) Any contract of employment under which a shop worker or betting worker who satisfies section 36(2)(a) was employed on the day before the relevant commencement date 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 on or after that date, or

(b) requires the employer to provide the shop worker with shop work, or the betting worker with betting work, on Sunday on or after that date.

(2) Subject to subsection (3), any agreement entered into after the relevant commencement date between a protected shop worker, or a protected 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, or

(b) requires the employer to provide the shop worker with shop work, or the betting worker with betting work, on Sunday.

(3) Where, after giving an opting-in notice, a protected shop worker or a protected 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 protected), his contract of employment shall be taken to be varied to the extent necessary to give effect to the terms of the agreement.

(5) For the purposes of section 36(2)(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, . . .