The UK is the world's largest producer and exporter of legal cannabis for medical and scientific use, according to a new report from a UN body.

Findings by the UN's International Narcotics Control Board (INCB) state the UK produced a whopping 95 tonnes of legal cannabis in 2016.

It is more than double the 2015 total of 42 tonnes and the UK's production now accounts for 44.9 per cent of the world total.

The report puts Canada in second place with 80.7 tonnes produced.

Some 2.1 tonnes was exported from the UK, making it responsible for 67.7 per cent of the world total, followed by the Netherlands (16.4 per cent).

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But campaigners have criticised the UK government saying they "consistently refused to allow medical cannabis in the UK on the basis that it has 'no therapeutic value'".

Medical cannabis products licensed in other countries remain illegal in the UK, even when prescribed by a doctor who has determined they are needed by a UK patient.

Steve Rolles, Transform's Senior Policy Analyst said: "It is scandalous and untenable for the UK government to maintain that cannabis has no medical uses, at the same time as licensing the world's biggest government approved medical cannabis production and export market.

"UK patients are either denied access and suffering unnecessarily, or are forced to buy cannabis from the criminal market.

"Countries with proper access to medical cannabis do not have this problem, as standardised cannabis products are in the hands of doctors and pharmacists.

"It is profoundly unethical, and a violation of the fundamental right to health, to deny people access to medicines that are prescribed by their doctors.

"The government must relax restrictions that grant a monopoly for a single product to a single company.

"It must allow access to cannabis-based medicines that serve patients needs - what they don't need is the government's cruel and misguided war on people who use drugs."

READ MORE: ‘Skunk’ dominates UK cannabis market, study finds

A significant part of the UK's legal cannabis production goes towards a cannabis-based medicine called Sativex.

Produced by GW Pharmaceuticals, it is available on prescription, but only via the NHS in Wales.

The issue of medical cannabis was highlight recently by parents of six-year-old British boy Alfie Dingley.

They say their son, who suffers from a rare form of epilepsy, can be treated with cannabis oil but it is banned in the UK Alfie, from Kenilworth, Warwickshire, returned from the Netherlands last month, where he had been receiving this treatment.

His parents have called on the government to let him use the medication in the UK.

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Since 2000, more and more countries have started to use cannabis and cannabis extracts for medical purposes, as well as for scientific research.

In 2000, total licit production was 1.4 tonnes; by 2016 it had increased to 211.3 tonnes.