Section 13 of the traffic rules state that:

"Drivers approaching pedestrian crossings must not overtake vehicles or trams which obscure any part of the view of the pedestrian crossing."

Furthermore, as you have an obligation to give way for any pedestrians wishing to cross the road at the crossing, and since visibility is obstructed (by the bus, blocking your view of the footpath leading up to the crossing) you should adjust your speed accordingly.