Sir; In his letter of July 27, Ben Ayliffe of Greenpeace accuses the Food Standards Agency of being mistaken and confused over GM labelling. We are neither. Greenpeace claims the threshold for GM content could be effectively reduced to 0.1%, but ignores the fact that the sensitivity of GM detection methods depends primarily on the material being tested. For example, tests on processed foods are far less sensitive than tests on raw materials and would not reliably detect GM content at this level. The FSA supports the idea of a single threshold, which would be enforceable across the entire range of foods tested, and by all EU member states. Additionally, we would not advocate a threshold for products such as oils, which do not contain GM material simply because of the likelihood of fraud. Greenpeace also claims that the FSA is confused over traceability. In fact, the agency's position is clear. We believe it is impossible to rely on a paper trail to establish the source of commodity crops grown on a large scale outside the EU. However, the proposed GM-free label could use this method to establish the source of products with a short, verifiable supply chain ­ similar to an assurance scheme ­ and would provide genuine choice for consumers choosing not to eat GM foods. The FSA disagrees with the draft EC proposals for labelling of GM foods because they are impractical and unenforceable ­ a view publicly echoed by UK enforcement authorities. By recommending that current EC labelling regulations for GM foods be maintained, the agency is not ­ as Greenpeace claims ­ pushing for weak labelling', but calling for labelling rules based on the detectable presence of GM DNA or protein in food so consumers are not given assurance that cannot be delivered. Geoffrey Podger Chief executive Food Standards Agency {{LETTERS }}