That is true, and why not also ignore the frictions created by a single currency, free movement of labour and people, or the harmonization of judicial systems during times of crisis. Surely under such strain, it is only fair that Germany no longer subsidizes Italian public debt, institute border controls for the transport of gas and oil, eventually instituting controls for all energy-derived products of any kind where a pricing inefficiency is being exploited by any neighbour. It would mean Putin responded to our sanctions by destroying 70 years of European cooperation, and doing so without even so much as firing a single bullet.

Energy is the economy, and the failure of an integrated energy market means the failure of so much more.