Complex sentence: They extended their lead to two-thirds of a length by Craven Steps but the bend in the river favouring Cambridge, the lead was halved, and by the Mile Post, the Dark Blues led by the length of a canvas.
Split into simpler sentences: They extended their lead to two-thirds of a length by Craven Steps but the bend in the river favoured Cambridge, and their lead was halved. By the Mile Post, the Dark Blues led by the length of a canvas.