Sadly, I'm not familiar with Aidan Chambers' Ghosts London Bus Story in detail. But if I were to speculate, it might be a story that uses the London bus as a setting to explore themes of the unknown, the past, and the supernatural. London has a long history and many old tales, so Chambers could have combined the idea of ghosts with the common experience of riding a London bus. It could also be a story that delves into the idea of how the ordinary can become extraordinary when the supernatural intervenes, like a normal bus ride turning into a terrifying or mysterious experience due to the presence of ghosts.
I'm not entirely sure specifically about Aidan Chambers' 'Ghosts London Bus Story'. It could potentially be a fictional tale involving ghosts on a London bus. Maybe it's a story about strange encounters or apparitions witnessed on a bus journey in London within the context created by Chambers.