When the Sunday working laws came into effect I worked for a place called Charlie Browns, basically a place like Halfords.
I and two others opted out simply because we were so cheesed off with how we were treated at the store. Retail truly sucks.
We came under a lot of pressure from the management. We were the only people to opt out in the whole chain.
The company skrewed up big time on all of this. You will find that large companies will simply tell you how they "think" work regs work. It doesn't mean they are necessarily true and they rely on people never actually testing their assumptions/ lies out.
We did and it resulted in the company having to recall and rewrite both the employee handbooks and change the wording of everyones new contracts.
It sounds petty and we actually lost money as we ended up only working a 4 day week.
Was it worth it?
Hell yes. Sticking it to a company that so truly deserved it was one of the most satisfying moments in my working life.
Asking the union about your options is a very good move. We three joined a union just to help us in this "battle" and they were really good and although the company didn't recognise a union they sure as heck recognised the legal representation the union gave us that ripped the companies illegal working practices apart.
Fond memories.