Mr Bingley's phrase "steer the punt from the Cambridge end", to describe lesbians, refers to the different practices used by Cambridge and Oxford university students when propelling punts on their respective rivers. Cambridge students tend to stand on the raised platform at the back of the boat, whereas Oxford students more often stand in the well of the boat with the raised platform at the front of the boat. If the boat happens to hit another boat or the river-bank, the well of the boat is a safer place to be standing as there is a greater chance that the punter will fall into the boat rather than out of the boat into the water. Evidently Mr Bingley is of the Oxford persuasion in that he regards the Cambridge practice as the unusual one.
An intrigued viewer will quickly research the fact the the series writer, Guy Andrews, is an Oxford man himself, as were Jane Austen's father and university-educated brothers. An informed Cambridge-punt-experienced viewer will recall that the Cambridge style is the more enjoyable, more stylish, as well as the more precarious choice.