If it gets to a point where a staff member has to quote the law, they've already lost, I think.
c2c excepted, a quiet word from the gripper normally sorts things if he's willing to have it.
I ask as a passenger rather than a staff member. In my experience, the most difficult passengers are those who assert that the Quiet Zone guidelines are not legally binding, concluding that they're not therefore obliged to comply with them (often with the twist that I'm violating the QZ by speaking to them...).
As I have never heard a contrary argument until reading this thread, I wondered whether the law has decided that these byelaws govern the Quiet Zone. Byelaw 7(1)(ii) ("use any instrument, article or equipment for the production or reproduction of sound") would, for example, seem to ban the use of mobile phones in any carriage where they annoyed anyone.
A related question, which may expose me as a newbie: do TOCs offer QZs entirely in response to customer demand, or is there any regulatory or legislative requirement that they're fulfilling?