The primary output of the SEA process is the Environmental Report, a document required by the SEA Directive which identifies the likely signifi­cant effects on the environment that would occur if the plan or programme were to be implemented (SEA Directive, 2001, Article 5(1)). Annex I of the SEA Directive sets out the minimum information that the Environmental Report should contain. Given that the SEA process is essentially a com­parison of the state of the natural and human environment with and without the plan or programme being implemented, the starting point of the Environmental Report is to identify the current state of the environment and how that area would evolve without implementation of the plan or programme (SEA Directive, 2001, Annex 1, paragraph (b)). The Environmental Report should also identify the broad environmental char­acteristics of the area likely to be affected, as well as the particular areas where impacts could be significant, such as biodiversity, population, human health, archaeological heritage and landscape (SEA Directive, 2001, Annex 1, paragraphs (c) and (f)).

Perhaps the most significant part of the Environmental Report, however, at least in terms of the ideological drive behind the SEA Directive, is the part which identifies the measures envisaged to ‘prevent, reduce and as fully as possible offset’ (SEA Directive, 2001, Annex 1, paragraph (g)) the sig­nificant adverse impact on the environment. Indeed, the SEA process would have very little worth if authorities were not obliged to consider ways to mitigate the serious environmental effects that have been identified by the process. These measures should be drawn up in light of current knowledge and methods of assessment and the contents and level of detail in the plan or programme so as to ensure that the local authority can identify mitiga­tion measures which would be commensurate with the nature and extent of the likely environmental effects (SEA Directive, 2001, Article 5(2)).

As well as identifying practical measures that would mitigate the envi­ronmental impact of the proposed plan or programme, the SEA Directive also requires the Environmental Report to identify, describe and evaluate the ‘reasonable alternatives taking into account the objectives and the geo­graphical scope of the plan or programme’ (SEA Directive, 2001, Article 5(1)). This requirement is designed to ensure that the authority gives serious consideration to the environmental impacts of the proposed activity and applies its mind to alternative plans or programmes (or variations on the existing plan or programme) what would have less serious consequences for the environment. On a practical level, the area of alternatives is often the most closely scrutinised by interested parties and, in the United Kingdom in particular, local authorities have been particularly cautious in their approach to identifying alternatives.