The NHS is exploring the possibility of making its own cannabis oil so that it can run trials into the drug’s use in treating epilepsy.

Medical cannabis has been legal since 2018, after a campaign by parents who said it helped to prevent seizures in their children. But in the 18 months it has been available no NHS prescriptions have been issued, partly because doctors are not convinced of its effectiveness. The result is that parents must pay for private prescriptions.

The Times understands that NHS chiefs have been critical of commercial cannabis oil manufacturers, who they say should run trials to demonstrate the product’s efficacy.

Given that they have not done so, Stephen Powis, NHS England medical director, said that the NHS was