Climate change and energy security have come to dominate the energy policy agenda. Concerns about energy security in the UK have been driven by the loss of self-sufficiency in oil and natural gas and a growing dependency on imports. This report explores ways of enhancing the “resilience” of the UK energy system to withstand external shocks and examines how such measures interact with those designed to reduce carbon dioxide (CO2) emissions. The concept of resilience is explored and a set of “indicators” is developed to define quantitatively the characteristics of a resilient energy system. In the report we systematically test the response of the UK energy system under different scenarios to hypothetical shocks. These are all assumed to involve the loss of gas infrastructure. We then assess mitigating measures which can help to reduce the impact of these shocks and test their cost effectiveness using an insurance analogy. The report covers one workstream in the larger UK Energy 2050 project conducted by UKERC.