"Are librarians always this much trouble?"
Yes we are!!!! O'Connell having a humurous moment with his wife on that double-decker bus in The Mummy Returns
Tower Bridge
Finally we go to Tower Bridge with the decapitated bus. I can’t tell you where the low bridge was where the accident happened as there are none of these in London that I know of in the right area. I have a sneaking feeling it was done at Sheperton Studios as it was a complicated and dangerous stunt not really suited to busy 24 hour central London.

If you take the film down to frame level (I was lucky enough to have a VCD to play with for a week) you will see one bus was taken up to the bridge, then there is a cut and another replaced it for the roof to come off – presumably a single-decker with one which the FX boys have added a temporary structure to the top of.
What I can tell you was the Tower Bridge run was taken with a crane camera from the north side of the river on the west of the bridge next to the Tower of London (marked with a cross on the map). If you look at the photo above there is a wood clad semi-circle on the base first tower of the bridge – this is the modern  Visitor Centre which has been covered to hide its posh glass windows.

When we see O'Connell running up the slope I think this is CGI and the jump Fraser did was presumably done at the studio and had the tower added in behind, but it makes for one of my favourite sequences.
Bus Ride Page