It's Topsy from Uncle Toms Cabin.
Thanks folks, I've been wondering about that for bleeding years.
You know as a youngster I read from my father's bookshelf. Mostly Dickens and Doyle, but there were a couple of Mark Twain's works and a few by other American authors. One book I can recall seeing the cover of though, was Uncle Toms Cabin. But for the life of me, I can't remember actually reading the tale.
Seems I must have, otherwise my mother or father must have referred to how Topsy grow'd colloquially.
Londoners' have (or used to have) a habit of coining descriptive phrases. So the words I can half recall must have been "Like Topsy, it grow'd an' grow'd!"