Certainly Nelson is the centrepiece of the shot. However on the right we can also see a certain Jedi Master named Yoda using the force to hover above the ground. (In reality, a street performer who would be standing on a plate which is attached to the walking stick, which would in turn be attached to a plate on the ground.) A civilian who is viewing Yoda forms the third point of the triangle.

For a little bit more symmetry, we have two towers off to the side of Nelson in the background. On the left is the Queen Elizabeth Tower (more commonly but incorrectly known as Big Ben) which was shrouded in scaffolding during our visit, and to the right is a domed building which I have no idea about. Of course, it's a complete optical illusion because in this shot those two seem to be about the same height... which clearly they aren't. The one on the right is in Spring Gardens, which is near Admiralty Arch just on the far side of Trafalgar Square, around 250 metres away, while the alleged "Big Ben" is closer to 950 m away.