I think allotment is the right word. They are intended for hobbyists gardeners, or at their inception during WW1, for families in the city to be able to grow mo

I think allotment is the right word. They are intended for hobbyists gardeners, or at their inception during WW1, for families in the city to be able to grow mostly potatoes. The size of sheds allowed varies a lot. Originally they were just meant to store garden tools (and potatoes). Many allow nothing more than 6 square meters.