Looking at the satellite view of some grassy rooftops in the city of London (the square mile), it seems to me that a sufficiently motivated wealthy person could keep several sheep in a more central location. Some of those roofs look like they have more habitat space than the most central sheep lives in.
A good many are known by filed dimensions, some are suspected to be larger than declared.
While a number may be urban bunkers, others ostentatious wealth displays for shoes, clothes, jewels, and rare collectables of the very wealthy perhaps one is home to a rabbit .. or a sheep.