In 1926, there was a ‘wall’ built on Valeswood Road/Alexandra Crescent (a private road) , to keep the inhabitants of The London Corporation’s estate in Downham out of Bromley (or to deter them from taking a short cut – thanks to Downham Estate Having Your Own Patch for the pic). The estate was built to house people moved out of the London slums when the post-war clearances took place. The houses are designed to be reminiscent of Kentish cottages.
History Today mentions it on their website, demonstrating that the concept of gated communities is not a modern one: by Michael Nelson, here. He grew up on the ‘wrong’ side of the wall in Downham.
"stood near the house where I lived as a child... the residents of Alexandra Crescent, a private road in Bromley, Kent, ... built a seven-foot wall, capped with broken glass, across the road. The wall was constructed to stop the working classes ... like our family, entering the streets of the adjoining middle-class estate."
Bromley was part of the county of Kent until the boundary changes of 1965, so the houses in areas of Bromley, still list ‘Kent’ in their addresses. When the boundaries changed, the Orpington residents were given a vote as to whether they wanted to join the new borough or not.