What is the irony in A Christmas Carol?

"A Christmas Carol" was written by Charles Dickens (small detail). It is ironic that Bob Cratchit toasts Scrooge for their meagre dinner. Scrooge, of course, treats Bob like a slave yet he still pays tribute to him. Scrooge describes his father as being rather cold, just like he is. I also recall the Ghost of Christmas Present repeating Scrooge's callous words, "are there no workhouses", when Scrooge inquires who will take care of the street kids that the Ghost shows him.