By Jessica Frank-Keyes Polls often narrow as the date of an election draws near. If the gap shrinks this time round, will it mean Labour won’t be able to secure the thumping majority it desires? Jessica Frank-Keyes takes a closer look As the clock ticked towards the end of this Parliament, and the inevitable general election, there was one graph that had come to embody this political moment more than any other. Two lines: one red, shooting upward then flatlining up high; and one blue, a sharp drop, and then, similarly fixed in place, bumping along – if not the bottom – then the graph’s lower h…