What carol is sung outside of Scrooge's office by carolers in Dickens' "A Christmas Carol"?

In the version with Patrick Stewart it was a lone caroler singing Good King Wenceslas.

That was a great clip from the 1951 movie reggie. You are right, there are many versions of the Scrooge story. Here is an extract from Charles Dicken's original story: "The owner of one scant young nose, gnawed and mumbled by the hungry cold as bones are gnawed by dogs, stooped down at Scrooge's keyhole to regale him with a Christmas carol: but at the first sound of - 'God bless you, merry gentleman! May nothing you dismay!' Scrooge seized the ruler with such energy of action, that the singer fled in terror, leaving the keyhole to the fog and even more congenial frost." Happy Christmas!