These photos are from two American Sweetgum trees located immediately adjacent to one another. Interestingly, at the time the photos were take (12 Sept 2014) only one of the trees had any "fruit" on it. I'm not sure why this would be the case but I'll follow up in the Spring to observe how each flowers.
Although London Plane trees (Platanus x Acerifolia) are very common in London, the Oriental Plane (Platanus Orientalis) is relatively rare. For whatever reason all the plane trees along the north side of High Street Kensington between Holland Park and Hyde Park are surprisingly of the Oriental variety.