One couldn't go to London and not blog about the London Plane tree, Platanus x acerifolia. It is the quintessential urban tree, tolerating high levels of pollution and root compaction. It grows to prodigious heights and casts a dappled shade. Its bark when younger than the veteran in this picture flakes into a mosaic of light greens and greys.
It's thought to be a hybrid between P. occidentalis, the American Sycamore, and P. orientalis, the Oriental Plane, but no one seems entirely sure!