Bill Hayden writes a cheque for his girlfriend and tears it out of the cheque-book. He then writes her name and address on a slip of paper. In the next shot he is shown ripping a (blank) cheque from the cheque-book and handing it to Smiley along with the slip of paper.
In the previous episode, Fawn's hair is shaggy and hangs over his ears. Now, a day later it is short and trim. He's been guarding the kidnapped Toby Esterhase for the intervening period, so he could hardly have run out and got it cut.
When Peter Guillam is testing the taping system at the safe house, he says the recorder is voice-activated, but it doesn't stop turning on his first silent pause, which is much longer than his second and third pauses, when it stops instantly.
When the passengers get off the train (36 min), they seem to be non-actors and look directly at the camera, especially the lady passenger who looks twice.