Whether this turn into a full house price crash depends on the banks - at the moment they're quite content to perpetuate this credit cruch, increasing their own profit margins at the expense of their customers. If they stop offering cheap mortgages to people with existing mortgages and now lower LTV's then quite frankly people will default on their mortgages. This decreases house prices even further, meaning more people won't have enough equity in their houses to get a deal, and so on. The banks will suffer from this as their assets (i.e. loans) are not worth what they are secured against (houses). It's in their own hands, but given the greed and short-termist attitudes of the city, I doubt they'll do the right thing.