If you stand on a planter made from old potato boxes in London’s most central city farm, you can see the flag flying from the Houses of Parliament. As a military helicopter rumbles overhead, two lambs caper around the yard. A pregnant sow snores in the shade. The animals seem remarkably blase about their high-profile location. “The animals enjoy it in London,” says farm manager Sally Scantlebury. “Some of them really like the attention. I…