The government’s former top drugs adviser on Wednesday called for scientists to have a free hand in determining the risks of illegal substances, as he denounced past political interference in the work of the advisory committee he headed.

Prof David Nutt, the former chairman of the Advisory Council on the Misuse of Drugs, who was fired last week by Alan Johnson, the home secretary, demanded an overhaul of the current system of classifying dangerous drugs, which he said should in future be run independently like the Bank of England’s committee of experts who set monetary policy.