The world’s largest cannabis company is putting down roots in Britain after drug laws were changed to allow marijuana to be prescribed to patients for medicinal use.

Canopy Growth, a Canadian grower that generated sales of C$80m (£47m) last year, has spent years researching the chemical makeup of marijuana and cultivating specific strains of the cannabis plant into a range of different strengths.

Its chief medical officer, Mark Ware, said a new UK subsidiary, Spectrum Biomedical, would begin importing and distributing cannabis to pharmacies at the request of physicians in the first half of 2019.

“We take cannabis very seriously indeed as a medicine,” he said. “We have as close to a pharmaceutical-grade product as we can without the approval.”

The potency of the drug can be controlled by varying the ratio of THC, the psychoactive compound that gives recreational users “high”, and CBD, the compound that relaxes people.