As genetically modified (GM) products approach the market stage, the UK government and agro-food industry have faced a suspicious or hostile public. Since 1998 many retail chains have undertaken to exclude any GM-derived ingredients from their own brand lines. This commercial blockage has intensified pressures for greater precaution, even for a moratorium on cultivating GM crops. Political protest has led to strategies for precautionary commercialization. Government and industry have cooperated to plan a 'managed development' of GM crops. Across the agricultural supply chain, industry has devised voluntary guidelines to ensure segregation of GM crops and to limit the spread of GM herbicide-tolerance. In particular UK regulators seek to test the risk that broad spectrum herbicide sprays could damage wildlife habitats; they have broadened the advisory expertise accordingly. These measures open up the precautionary content to further debate, at both national and EU levels. Market-stage precautions establish a means to test claims that GM crops are environmentally-friendly products. By translating public concerns into broader risk-assessment criteria, the UK procedure involves critics in potentially influencing standards of scientific evidence and environmental harm. This social process has become a prerequisite for legitimizing commercial use.