Subject to subsection (2), a shop worker or betting worker is to be regarded as "opted-out" for the purposes of any provision of this Act if (and only if)—
he has given his employer an opting-out notice,
he has been continuously employed during the period beginning with the day on which the notice was given and ending with the day which, in relation to the provision concerned, is the appropriate date, and
throughout that period, or throughout every part of it during which his relations with his employer were governed by a contract of employment, he was a shop worker or a betting worker.
A shop worker is not an opted-out shop worker, and a betting worker is not an opted-out betting worker, if—
after giving the opting-out notice concerned, he has given his employer an opting-in notice, and
after giving the opting-in notice, he has expressly agreed with his employer to do shop work, or betting work, on Sunday or on a particular Sunday.