Went on the Big Bus Tour Saturday 20th July, just great to hop on & off.
All the staff where very polite, didn't have to wait very long for a bus.
we used the headphones ( FREE ) and you can adjust the volume
plenty to see with good information, would I recommend it YES.
Also if you have time, go for afternoon tea on the Thames, it is just the best ever.
We went with Bateaux London