We explore the relationship between low-carbon objectives and the strategic security of electricity in the context of the UK electricity system. We consider diversity of fuel source mix to represent one dimension of security-robustness against interruptions of any one source-and apply two different diversity indices to the range of electricity system scenarios produced by the UK government and independent researchers. Our results show that low-carbon objectives are uniformly associated with greater long-term diversity in UK electricity generation. With reference to data on wind generation we also consider the impact of source variability on a second dimension of security-the reliability of generation availability. We conclude that this does not undermine our fundamental conclusion that low-carbon scenarios are associated with greater strategic security of supply in UK electricity. We discuss reasons for this result, explore sensitivities, and briefly discuss possible policy instruments associated with diversity and their limitations. (c) 2005 Elsevier Ltd. All rights reserved.