Thorny and thornier still - I'm an avowed atheist, but see nothing wrong in the CoE expressing an opinion over upcoming legislation or regulation, so long as they do not expect to have a disproportionate effect on the making of that law (which, granted, they are an established church so do have more clout than they ought etc). Like any other clump of people or institution, it has a particular worldview which it wishes to advance and, though I may disagree with it, I respect the church's right to put it forward.
Likewise, I'm sure all sorts of charities put their views forward when it comes to legislation, even though they are not democratically elected.
That said, we live in an increasingly secular society where church attendances are dropping - Sunday is no longer just a day of worship and peace. The pace of life e'er changes.
That said, even though I'm an atheist, I appreciate the comparative break Sunday brings and feel sorry for all those retail workers who will not be able to contest this. While it may give some choice and leg-room for the likes of Tesco et al, individual workers will have little to no choice over their hours - thus, they are likely to be robbed of what little peace they get on Sundays. Shame, really.