personaly i would never have more then a few per acre in london as it is very poor in flowers, its all grass and concrete and small gardens, untill your into the suburbs.
where as in brum its well over 30 plus a garden,
where i am its not the grass lands its the gardens, london with its great park lands, they are full of grass and trees not flowers, brum is a lot more flowers, the canals alone give a massive acreage of land of wild flowers,
within the square mile of my address i am aware of and only aware , may be theres more? but there is 110 that i know of