Also planning laws; if ~8 story blocks of 3 bed flats were built the dynamics of London's market would be completely different. These would be ideal for families and the density & low construction cost per unity would mean that the supply of family homes in the market would seriously improve. As it is apartments in London are almost exclusively 2 bedroom where one of the bedrooms is small. This is ok for a family with a baby, but untenable (by law) for a family with two kids over 8/9 (can't remember) who have a biologically different gender (no judgements from me - I just believe that this is UK law as currently written). This creates pressure in the housing market for single dwelling footprints - which are mostly used and poor by modern standards (but mind-blowingly expensive).