As part of its legal commitment to reducing CO2 emissions, the UK has outlined a roadmap for significant increases in the use of ground source heat pumps for heating and cooling buildings. The technology is particularly suitable in new buildings, and in large commercial buildings. Such development is focussed in urban areas of economic growth. This paper presents an aquifer scale model of the impact of the expansion of open loop ground source energy schemes deployed in London. The model predicts the impact for currently operating schemes, and also the potential impact of all open loop schemes that have been licensed in central London. It is concluded that there will be thermal interference between these schemes and that in areas with such a high density of ground source energy schemes, the resulting loss of efficiency will mark an effective limit to the energy available for unbalanced ground source cooling. The current unregulated approach to managing the energy resource of the Chalk aquifer beneath London will not be able to sustain the demands implied by the UK roadmap for ground source energy. A more actively managed approach is needed if these energy demands are to be met, economically, in London and other centres of economic growth. (C) 2013 Elsevier Ltd. All rights reserved.