I wonder if there was any sub-surface element to that shelter.
The paving slabs appear to have been cut away in a large key hole pattern so perhaps giving a hint to a space below.
Whatever the case, the sound of lumps of shrapnel hitting the metalwork would have been terrifying.
It's difficult to tell exactly where the picture was taken but I suspect I'm not too far away in this Streetview link.
Marlborough Road