Why even go to that poker game?
You need £100 000 to play, the game is not only hosted by a crime boss, but he's also playing at the table. He controls the building, has men working for him inside and he cheats. The protagonists don't know that, but since they are con artists and thieves, they should have been suspicious. Even if you win, how can you even know you'll walk away with your gains?
Of course, this is what sets the whole film in motion, but it is hard to believe that small times criminals would risk their "life savings" that way.