It really depends on the company and the employment contract and when you were employed. For example my employers cannot force me to work bank holidays at present, but in the same organisation some colleagues are call centre staff and they may have to work, but get enhanced rates and I think they get additional holiday.
Most good employers will try and give people the choice where possible despite the contract, but at the end of the day they have to also provide the service that customers demand, and although I personally think the world would not end if the shops were shut from lunchtime on Christmas eve to the 27th, (and overnight for that matter) judging by the number of people that do shop outside these times I am maybe not your average shopper!
It amazes me that we ever survived when the only shops open on Sundays were garden centres and newsagents!