In British English, is it acceptable to address a professor as "Dear Professor X" when writing a formal or informal letter? Does it sound natural?
Why I am asking this question:
I was looking through the list of differences between the British and American editions of the first Harry Potter book by J.K.Rowling.
In the first chapter of both editions, a character named Hagrid keeps addressing Professor Dumbledore as
Professor Dumbledore, sir.
However, when Hagrid writes a letter to Dumbledore, the two editions use different forms of addressing:
Dear Mr Dumbledore
Dear Professor Dumbledore
Edit: Everywhere else in the U.K. edition, he is still "Professor Dumbledore". This letter seems to be the only exception. If he normally calls him "Professor", why he would write "Mr" in the letter?
Why "Mr" instead of "Professor"? Is "Dear Professor X" inappropriate in the U.K. for some reason? Or it just doesn't sound natural?