UK natural gas system integration in the making, 1960–2010: Complexity, transitional uncertainties and uncertain transitions

• ‘System integration’ as a complex social process.
• Technological systems and infrastructure networks are characterised by both ‘horizontal’ and ‘vertical’ integration.
• ‘System integration’ in natural gas industry was closely linked with governance patterns.
• Control technologies in the natural gas grid were introduced to reduce uncertainties but increased system's complexity.
• Governing ‘system integration’ in the UK natural gas regime was substantial for the regime formation.

The article focuses on the development of the natural gas system in the UK from its establishment to the present day, as an analogue for the challenges of integrating large, infrastructural technical systems for a sustainability transition. It is inscribed within the multilevel perspective approach yet concentrates on ‘system integration’ as a complex and uncertain socio-technical process. The case study focuses on two interrelated transitions in order to provide a co-evolutionary and comprehensive understanding of the uncertainties in system development and integration faced by the UK natural gas industry. Through thick historical analysis of the gas grid transition we provide insights into the sustainability of similar network technology transitions. At the same time we contribute to complex systems modelling approaches (broadly defined to include quantitative and qualitative modelling) by unravelling the roles and agencies of actors, institutions and technologies in the modelling and making of sustainability transitions.