I'm afraid being called "sir", or an employer who wants me to call somebody "sir" is something I find particularly objectionable.
A subject of Great Britain is only entitled to be addressed as "Sir" if he holds a Royal Commission or Royal Warrant in the Armed Forces or Civilian Services. Other Ranks, of which I was one when I served, are not entitled to be addressed as "Sir" unless decorated by Her Majesty.
Civilians engaged in commerce certainly do not warrant the term "sir".