Gbun and butty, I hope what I want to say applies to both! I found both your replies interesting, in part because they illustrate how different people feel about formality and what it means, how it is perceived, and so on. Perhaps there is something about me that just invites people to use my first name? On initial introduction, my surname is often used, but it doesn't last. I don't think that's any sign of disrespect towards me, but rather my lack of feeling superior or inferior to anyone whether their 'station' is traditionally thought to be below me or above me. It's not a simple lack. I've worked on it. I refuse to feel inferior or superior to anyone because, for me, feeling either of those things is the definition of being a snob, which I don't want to be. Most of my relationships with people are about exchanges of knowledge and experience. There are inequalities, obviously, but only as the result of the accidents of birth, education and experience. As far as relating to other people on a personal level goes, we're all equals in my view.
The end result is that it doesn't bother me one jot which way people choose to address me, so long as they are polite. I don't regard the use of my given name by anyone to be impolite. It seems some people do mind being called by their first name. So be it, but I'm glad I don't. Something else I don't need to worry about. Shrug.