There's an overhanging roof at the northern end of Hammersmith bus
station. It carries warning signs, and buses pass quite near it as
they
go past stop A. I'm not sure what route the number 10 takes around
the
bus station, I wonder if that might possibly have caused the damage.
If
so, it would be the offside that would have got hit worst.

IIRC, the buses go around anticlockwise at Hammersmith. The 9 and 10
routes enter from the South, and drop passengers at F, then they
usually park up against the wall opposite stops F and G, which often
involves a full lap of the station. They then pick up at stop H and
exit from the Northern exit. The overhang is opposite stop A IIRC, so
the bus would have been empty if it hit there. The other possibility is
that it was diverted onto an unfamiliar route and the driver missed a
turn somewhere.