Threadneedle is the first economic simulation framework to incorporate an accurate model of the banking system´s double entry book keeping and regulatory frameworks. Threadneedle allows us to create simple economic experiments which allow us to explore how the complex network of money and credit flows created through the banking system interact with market pricing systems. In this talk we will explore the behaviour of the banking system in market based economic systems, and discuss the thorny question of where the real causes of the periodic economic instabilities we experience as credit crises actually lie.