Doctors should be able to prescribe medicinal cannabis, the government’s chief medical adviser has said, paving the way for a change in the law within weeks.

Dame Sally Davies said that the rules on the medical use of cannabis were “very difficult to defend” as there was “conclusive evidence of the therapeutic benefit” for some conditions. Her conclusion will now be examined by the government’s official drug advisers, who will deliver their own report within three weeks.

Ministers say they will be led by expert evidence, with doctors, researchers and campaigners welcoming signs of imminent change.

Sajid Javid, the home secretary, ordered Dame Sally to review the rules on cannabis products last month after a series of cases where children were denied access to cannabis