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).
Odd - I thought that there were; I stand corrected.
In any case I think that a three bedroom apartment is viable for a family, whereas a two bedroom apartment where one of the bedrooms is very small isn't really.
If the planning laws were changed and a couple of thousand were built then the market prices would come down. Developers would still turn a profit because the cost of building is ultra dependent on the cost of land in London, which if the planning laws were changed would change.
Buy prices are already slighly down compared to 2 years ago, something to do with Brexit.
There are literally properties being built everywhere. Just take the overground to any direction and look around you. It doesn't make prices go down. There are too many people and too much money.
The issue is that these are properties that suit single young professionals /couples and speculators. This creates scarcity in the middle of the market and drives onward pressure for family dwelling units. In turn the pressure for family dwelling units drives cash-in-and-commute out to the home counties. All of which hollows out communities and the city - schools and infrastructure suffer much.
Prices are also down because of tax - sharp tax; which is a good thing in terms of dealing with speculation.