East London 18500 (LX55HGC) is a very special Alexander Dennis Enviro400. It is the bus purchased to replace the Dennis Trident, 17758 (LX03BUF) destroyed in the 77 terrorist attacks.
The Enviro400 is not a Stagecoach standard, but a stock vehicle, so is a bit of a one off in London terms. It was launched by the Mayor of London in October 2005 and christened Spirit of London.
These pictures of Spirit of London were taken when it made its debut at SHOWBUS in 2007.