St George is difficult to interpret. His sword stands point-down in front of him, surrounded by supplicating figures. He holds an amorphous object - the dragon's head?
Britannia also has a sword and supplicating figures, and seems to be holding chests of some sort. The profits of sea-borne trade?
Most oddly, the balance has the Monarch's crown on one side and a working man's flat cap on the other.
Frankly, the symbolism eludes me.
It doesn't seem to be known who did the other sculptures on Thames House, but they are not nearly craggy enough for Jagger.
The keystone over the visitors' entrance is indisputably Old Father Thames (again), wearing a shell with dolphins on his head. On either side spreads boating paraphenalia including sails, oars, boathooks, lifebelts and mooring chains. The swags of flowers presumably symbolise the prosperity the river brought to London.