The case for maintaining or improving the defences of agricultural land is assessed in a similar way to other assets. DEFRA's policy statement on the appraisal of flood and erosion risk management underlines the need to value agricultural land and the damages that can occur as a result of flooding and erosion. Specific guidance was provided by DEFRA in 2008 based on HM Treasury Green Book appraisal principles. It takes account of the decoupled Single Payment Scheme introduced in the UK from 2005. Grant in aid is assessed according to the whole life economic, social and environmental benefits of a scheme. Where these benefits include the protection of agricultural land, grant in aid is calculated on the basis of the economic damages avoided to the agricultural property over the lifetime of the investment, valued in line with HM Treasury guidance. The relevant rate at which these benefits attract grant in aid is 5.56p per £1 of qualifying benefit, i.e. 1/18 of the damages avoided.