We are all much more relaxed nowadays about how we address one another: your plumber won't care whether you call him Mr Chrascz or Sid, assuming that those are his names. Formality is acceptable in any circumstance and we can all judge when informality is considered improper—senior members of the royal family, for example would probably be a bit miffed if you used their first name on first acquaintance and you would be justifiably offended if they did it to you.
The other day I had to see a consultant surgeon (nothing serious), who introduced himself as "Mr Smith", and then proceeded to call me "Tony". Was he just socially inept, or trying to put me at my ease, or was he speaking de haut en bas? I do not know, but I failed to warm to him; next time I will ask someone else to give me an opinion on the surgical options for my obstreosis of the ductal tract (tertiary, but only mild), first looking him up in the register and then greeting him with an outstretched hand and a cheery "Hello, Arthur!"
This encounter was in the back of my mind a few days later when I telephoned the Council's Rubbish Disposal Hotline to ask about having the remains of our demolished garden shed taken away. The telephonist grasped the problem immediately, and said, "Right, I'll put you through to Bulky Waste".
This summoned up a mental picture of the honest fellow, a little overweight, certainly, but fit and alert, ready at a moment's notice to send out one of his crack teams to the aid of desperate householders unable to get out of their front doors because of all the broken boilers and old mattresses blocking their hallways.
However, the transferred call was answered very quickly so I didn't have time to worry about whether I should open the discussion with "Good morning, Mr Waste" or "Hi there, Bulky!"