This really happened to one bus driver, Albert Gunter, on the evening of 28 December 1952. He was driving the number 78 to Dulwich, a busy double decker, when something went wrong and he found himself on a rapidly opening bridge. Amazingly, the driver had the nerve to accelerate and jump the gap between the two bascules. The bus made the leap - about 3 feet by that point - successfully, and nobody was seriously injured. Albert Gunter received a reward of £10 for his bravery.
Sadly, there is no photo of the event but here's a (non-) artist's impression!