The trumpet player was something odd, but I'm guessing from the second the first woman started singing what I assume is a happy birthday song the message would have got through to the driver. It also seems like most of the passengers on the bus were in on it.
It'd never happen over here for many reasons, but still I don't work in London so feel free to send an orchestra on my bus. It's empty most of the time and I'm pretty much always late :o)-