Time is traditionally five minutes behind Greenwich Mean Time.
This tradition dates back to the days before the railways when each region of the country kept to its own local time. Hence what we now call Cathedral Time is actually a survival of old Oxford Time. With the coming of the railways, distant parts of the country which had once been isolated from one another were now linked, and it was necessary for railway stations to keep to the same time. The problem stems from the fact that the earth spins on its axis once every 24 hours. Because it spins, different parts of the earths surfaces face the sun at different times and even the difference of a few degrees in longitude can affect the calculation of time in two relatively close places.