Issues of confidentiality aren't here nor there, employees have the legal right to discuss salary for the purposes of determining whether "unfair pay" (gender discrimination etc) is occurring, which basically renders clauses relating to the discussion of salary moot.
I think I said this previously but NEVER tell anyone at work what you get paid, if you believe you are not paid enough build a case ask for a raise or leave and get another job.... two very simple options... if those two options are not on the table then I would expect the person involved knows full well they cannot get another higher paid job... or there are other benefits at the current job they are not willing to loose (close to home, flexible working etc)
You don't need to know what the company pays other people, you can look at the job market to see what the going rate is...