Hi Tamguatlay,
I am not Nona, and you probably won't trust me because I'm not a native speaker of English. I only wanted to share my experience, which can add something to the topic.
As an ESL student of BrE, I was taught to end a letter with "
Your faithfully" when it addresses an unknown addressee (i.e., when it begins with "
Dear Sir or Madam") and with "
Yours sincerely" when you know his/her name (i.e., the letter begins with "
Dear Mr/Ms/Miss [+surname]").
However, during my year in the UK, I saw the expression "
Your faithfully" only twice, in two letters written by members of my University staff. Funnily enough, the first one began with "
To whom it may concern" (another extremely rare expression
) and the second with "
Miss [+ my surname]", two opening formulae I was taught NOT to use, when having classes
... none of them actually began with "
Dear Sir or Madam"! Both the letters I mentioned (I've still got them) come from a University, so I'm obviously not talking about illiterate writers.
Another thing I can say is that my British teacher on the one hand strongly advised us to close formal letters in our CAE and CPE exams with "
Yours faithfully" or "
Yours sincerely" (depending on the circumstances) because those were the expression the examiners were looking for. On the other hand, he also warned us that these day most people, also in the UK, will close those letters with "
Sincerely", "
Regards", "
Kind regards".
If my experience is anything to go by, what we learn sometimes can differ from what is actually done nowadays, just as Clive said.