http://southeast.greenparty.org.uk/news.html#SEPlan says:

A lack of urgency with regard to climate change. We need to achieve cuts in greenhouse gas emissions of over 85% by 2050 to avert major changes in global climatic conditions. We note that the SE is likely to be exposed to the most serious effects of climate change in the UK. Since the draft plan also notes this, we are concerned by the lack of adequate measures to address this problem especially with regard to surface transportation, aviation expansion and building standards. We note that the Institute for Public Policy Research calculates road traffic will be up 25% by 2015 in the SE, water use up 15% and air pollution by 7.5%.

They go on to list further reasons for opposing the South East Plan mainly criticising infrastructure and resources along with energy conservation. It looks like they don’t trust all the promises that are being made with regards to the South East Plan.