This paper explores the nature and type of evidence employed by participants in an issue of public concern. By examining documents and interviewing members of the public involved in the debate, the way in which evidence was used in the arguments for and against the issue was determined. Three dimensions of evidence emerged from the data: formal scientific evidence based on the data; informal evidence (e.g. common sense, personal experience) and wider issues which impinge on the evidence (e.g. environmental or legal concerns). In this particular controversy, it was the questioning of the formal evidence by local scientists which became the 'magic bullet' but pertinent questioning by local nonscientists also framed the debate. The authors suggest that school science curricula should include practice in questioning and manipulating different sorts of real data in a variety of ways so that pupils are equipped and empowered to tackle contemporary issues of this kind.