On Start the Week Andrew Marr asks how far scientific evidence can influence the political agenda. Professor David Nutt is a respected researcher working in the field of drugs, but is best known as the government advisor who was sacked by the Home Secretary for comparing the risks of horse-riding with taking ecstasy. He argues for a rational debate on drugs policy based on objective evidence. Mark Henderson despairs that this will never happen while only one of our 650 MPs is a scientist. But the former Labour minister, David Blunkett, defends his profession, arguing that even evidence-based policy must take into account public opinion and perception. And for former No. 10 advisor Jill Rutter evaluates the evidence for and against.