In Chapter 10 of Dickens's Great Expectations, Pip goes to the pub to find Joe, as told by his sister. When he enters the pub, Joe and Mr. Wopsle are sitting at a table next to a mysterious man:
He was a secret-looking man whom I had never seen before. His head was all on one side, and one of his eyes was half shut up, as if he were taking aim at something with an invisible gun. He had a pipe in his mouth, and he took it out, and, after slowly blowing all his smoke away and looking hard at me all the time, nodded.
Pip would have immediately recognised him if it was Magwitch, considering the trauma he caused him, so it probably isn't. Is it Compeyson? If it is we don't get the tell-tale detail of the large scar across his face that defines his appearance in the rest of the novel.
The man then indicates for Pip to sit next to him and Pip declines. Then he proceeds to 'grill' Joe about who Pip is after he hears his name:
The stranger looked at me again - still cocking his eye, as if he were expressly taking aim at me with his invisible gun - and said, "He's a likely young parcel of bones that. What is it you call him?"
"Pip," said Joe.
"No, not christened Pip."
"No," said Joe, "it's a kind of family name what he gave himself when a infant, and is called by."
"Son of yours?"
"Well," said Joe, meditatively - not, of course, that it could be in anywise necessary to consider about it, but because it was the way at the Jolly Bargemen to seem to consider deeply about everything that was discussed over pipes; "well - no. No, he ain't."
"Nevvy?" said the strange man.
"Well," said Joe, with the same appearance of profound cogitation, "he is not - no, not to deceive you, he is not - my nevvy."
"What the Blue Blazes is he?" asked the stranger. Which appeared to me to be an inquiry of unnecessary strength.
If it is Magwitch, he would not need to ask all of these questions since he had met Pip and knew his name as well as meeting Joe when he was captured in the marshes as a runaway convict, so I don't think it is him.
The man also mentions this at the pub, when he is told Mr. Wopsle is the church clerk:
"Aha!" said the stranger, quickly, and cocking his eye at me. "The lonely church, right out on the marshes, with graves round it!"
This detail supports that perhaps it was Magwitch, since he first appears and meets Pip there, but Compeyson was also loose on the marsh near the church as he was recaptured whilst fighting Magwitch.
Finally, the man begins to stir his rum and water with the file that Pip had given Magwitch to break his shackles at the very beginning of the novel:
He stirred his rum-and-water pointedly at me, and he tasted his rum-and-water pointedly at me. And he stirred it and he tasted it: not with a spoon that was brought to him, but with a file.
He did this so that nobody but I saw the file; and when he had done it he wiped the file and put it in a breast-pocket. I knew it to be Joe's file, and I knew that he knew my convict, the moment I saw the instrument. I sat gazing at him, spell-bound.
It's strange that he was asking Pip's name just a few minutes ago but is now showing him the file, a very pointed symbol of Pip's frightening encounter with Magwitch in the first chapter. Maybe he was making sure it was Pip and not another boy? (this possible unsureness and need for clarification suggests is is not Magwitch)
Since he only let Pip see on purpose, he must either be one of the convicts or a messenger from the convicts. Either way this is a dramatic device used by Dickens to foreshadow the reappearance of Magwitch in Chapter 39 (when he reveals himself as Pip's mysterious benefactor, because he just before he leaves the pub he gives Pip some coins wrapped in two one-pound notes, which symbolises Pip's imminent unexpected inheritance) but is it actually one of the convicts? We know that Magwitch was eventually deported to Australia somewhere between Chapter 5 (when he is arrested in the marsh just after Christmas dinner) and Chapter 39. It is not stated when he does leave the country, but surely after his arrest to the prison ship he would not have been able to be at the pub, which is another consideration that seems to suggest that it cannot be him.
Is there any evidence in the book (or comments by Dickens) that points to who this man is?