I think London is a very big place! There is some evidence of prices reducing but not if the property is well located, in good condition, desirable and near transport links. Houses are reducing more than flats in some areas. The lower end of the market is still bouyant if the property is in the right place, in good condition and well priced.
Additionally, in London, there are enough wealthy people to give money to their offspring for a deposit. A very healthy deposit. Lots of young people see their future careers in London. They cannot get the same career elsewhere, or the same lifestyle and social life. All their friends might be in London so it's a big decision to move out. Many want some free time and not a massive commute, so pay for that privilege.
Nurses and teachers can easily buy in cheaper areas of the country. Two teachers, 7 years into their careers earning around £30,000 each, can buy in many areas of the country without too much hassle. Obviously the deposit is the problem, but many parents do step in to help. Anyone in the public sector who is on a career grade is perfectly Ok too nearly anywhere other than the home counties and London.
Another shortage of housing is caused by divorced people maintaining two family houses so each can have the children. Plenty of peope do this but it causes shortages.