Everywhere you look, the tale is always "property prices up!". I am sure that this is true for the vast majority of the country and for many parts of London. Of course it will depend on the property type too.
But from where I am writing and from the experience of many friends working in the City. Flats in Zone 1 and Zone 2 have essentially stagnated in value over the last ten years.
Looking at the sold data for my Georgian terrace (all flats) and streets across Central London. Flats sold for 600k in 2013 are now selling for 620k.