The Size 2 Gladstone is the largest of the Gladstone series of lanterns by Metcraft, as I cant find a Gladstone Size 1 in their current catalogues. The Size 2 Gladstone was designed to be mounted at between 9m-12m above ground-level. Perhaps this is the reason that there doesn't appear to be a size 1, in that the size 2 occupied all of the size 1's specifications - thus it was no-longer needed.

London

These Metcraft Gladstone Size 2s exist along Spur Road outside of Buckingham Palace. This place is a bastion for Metcraft lanterns, as they are mostly responsible for refurbishing and installing street lights along the roads here. 

These were installed between 2022-2024.

Another Gladstone Size 2 located on the other side of the road: