It also implies that the coverage of the policies needs to be as wide as possible in sector terms, so that it covers all fuels giving rise to carbon emissions, in all parts of the economy, and not just particular sectors. Without this condition there is again a risk of distortions.
 This expression of the idea is acknowledged to Michael Grubb, speaking at a BIEE Climate Policy Seminar.
 Valuation of energy use and greenhouse gas emissions for appraisal and evaluation. October 2011. DECC and HM Treasury.