The factors behind diverging long term growth experiences are diverse and difficult to disentangle, ranging from institutional and cultural aspects to economic conditions. This paper models the microeconomic relations between five dimensions of the long term process of structural change of an economy---organisation, technology, and sectoral composition of production on the supply side; distribution of earnings, and the related evolution of consumption patterns on the demand side---as the explanans of these different patterns of economic growth. We refer to a number of studies and empirical accounts of the history of the industrial revolution in the UK to set the model's foundations, and we analyse the model via numerical computation. Changes in the composition of workers-consumers related to the increase in firm size and organisational change induces product heterogeneity and firm selection, and the supply of new goods that satisfy less basic needs. Both selection and the emergence of markets increase market concentration, inducing capital investment accompanied by increasing labour productivity. Reduced cost then increases the demand of all consumer classes. Changes in firm size and organisation, investment, product innovation, and in expenditure shares of emerging classes, reach a critical point in which the economy transitions from slow to modern growth.