British medical cannabis companies are lobbying the government to ease restrictions around importing and exporting the drug, warning that they hinder growth and will force them to shift investment outside the UK.

Marijuana was approved for medical use in the UK in 2018, following a public outcry in response to headlines that children suffering from epilepsy were having to travel abroad to access cannabis-derived treatments.

However, companies in the sector complain that speedy legalisation has been hampered by excessive red tape and argue that the UK risks falling behind in an industry that is rapidly expanding in Europe, buoyed by increasing interest from investors in Canada and the US.

Groups can currently only import cannabis to fulfil existing UK prescriptions, and the Home Office will not issue export permits for most cannabis-based medicines.

“We’re hoping to raise series C funding of up to £15m in the next months, and all of that will be spent in the UK if we can export, otherwise we will have to go to Denmark, Portugal, Holland or Germany,” said Ben Langley, chief executive of three-year-old start up Grow Biotech. The company, which makes and distributes cannabis medicines to patients with prescriptions, wants to expand its manufacturing capability.

He pointed to the UK’s trade ambitions following its exit from the European Union and said the country’s strong reputation in pharmaceuticals could make it a “market leader” in the medical cannabis industry “except for the part that we cannot export”.

Current importing rules were leading to long wait times and higher costs for patients, argued Scott Maguire, chief executive of London-based Cannaray, who added that medical cannabis was expensive to access in the UK as few companies were licensed to grow it.

“We’re now establishing our supply channel in Canada because we haven’t been able to do so in the UK,” he said, an investment which is worth about £10m.

Mr Maguire said that Cannaray, which also sells cannabis-derived CBD drops for which no prescription is required, had diverted investment into the development of its medical cannabis business into Germany rather than in the UK “due to import rules”.

The Home Office declined to comment on whether it was reviewing its medical cannabis regulation.

Stephen Murphy, managing director of consultancy Prohibition Partners, said the British medical cannabis market was unlikely to turn over more than £10m this year, in contrast to Germany where he said more than €15m worth of medicinal cannabis was being sold each month.

But, in contrast to its relatively slow uptake of medical marijuana, Prohibition Partners said that the UK had become the world’s second-largest market for the cannabis-derived molecule CBD, which unlike tetrahydrocannabinol, or THC, does not make users “high”.