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—
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—
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.
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For the purposes of section 41(1)(b), the appropriate date—