Considering how temperate the London climate is, it’s amazing how much mileage the London locals get out of the subject.  The truth is that summers rarely get really hot and the winters aren’t really cold. In fact, it’s impossible to say with any certainty what the weather will be like in any given month. May might be cold wet and grey one year and gloriously hot and sunny the next; November stands an equal chance of being crisp and clear or foggy and grim. So, whatever time of year you come, be prepared for all eventualities, and bring a pair of comfortable shoes, as, inevitably, you may find that you're doing a lot of walking.