What happens to scientific objectivity when it enters the realm of public debate and policy, and is asked to inform and guide the choices made in that realm? Surely consulting science in making policy is done with a view to making policy decisions more reliable, and ultimately more objective. Evidence-base policy is a typical example of this approach. However, in these contexts scientific evidence is normally, and often inevitably, taken into account alongside other relevant factors (political, social, economic, ethical, etc.). Such complex practical interactions constitute a challenge both for the very objectivity of scientific evidence (how far should science let extra-scientific factors interfere with scientific facts, without endangering the objectivity of evidence?), and for the objectivity of the role of the scientist as expert in the policy-making process. In this paper I address – with the help of a case study – the way by which science contributes to achieving objectivity in policy making, and argue that objectivity, though not exhausted by what scientific evidence contributes to it, still retains a crucial and meaningful role in public debate.