PPS4 Policies - Public forum - Planning Advisory Service (PAS)

Tanya Leeds City Council considered edge-of-centre applications from Tesco and Asda earlier this week. Asda gained approval and Tesco was refused on the basis of the sequential approach outlined in PPS4. I'm not sure about the decision notice but PPS4 policies are referred to in the officers' report which can be found here: http://democracy.leeds.gov.uk/Published/C00000125/M00004642/AI00024522/ReportbyColliersCRE.pdf

Does anybody have advice on how to conduct an impact assessment of a retail planning application? The practice guidance associated with PPS4 is less than informative in this respect, especially with regards to 'locally important impacts' (EC16.1 f)? I am particularly interested in how one might appraise impacts on social and environmental sustainability grounds e.g. in terms of limiting carbon dioxide emissions, preserving/promoting consumer choice and promoting sustainable development? How much weight can be given to individual impacts? Is this up to LPAs to define through their development plans? Is there any guidance on this subject anywhere? Any help appreciated, Simon