I'm really interested by their body language in the pictures. In season 1, there's a lot of space between Benedict and Martin, and Martin has his arms crossed, signifying slight discomfort (though he could just be cold). Season 2, they're closer and have more open body language, showing they're more comfortable with each other. Season 3, they're in each other's intimate space (very close - touching), showing they're very close and comfortable with each other. I love it!
nerding out over the tube map behind them.. paths are accurate, even if names are changed!! :D