It almost happened in Cathles road, Balham a couple of years ago. Cowboy builders removed all internal walls and dug a basement without under pinning. Funnily enough the wall at the back started falling out and the walls of neighbouring houses started coming in. Wandsworth council shored up the building with £100k of concrete into the basement. The building and its neighbour have recently been sold at auction. It’s very possible even locally. Who knows what will happen when they start the building at the two hotels on the common with their proposed iceberg basements.