Thanks
lang rabbie There could have been another two lions on another gate on the library side of course.
I suggest a hypothesis. In one of Lambeth's many moments of madness they decided to remodel the library gardens making them more open.
And when they got rid of the gate they were loath to "waste" the lions, they simply redeployed them - and allowed them to get nicked later on.
People of my vintage will recall there were two raised grassy areas with some shrubs - to the left and right of where this entrance is, held in by a low brick retaining wall.
But there was no entrance, and the gardens were paved over with bog standard paving slabs.
Except for Tate's bust + lions, which I recall as being more centrally located - that is further back from the camera than here.