Media playback is unsupported on your device Media caption Opinion is divided on whether banning khat in the UK is the right thing

The leafy plant khat, which acts as a stimulant when chewed, is about to become a banned class C drug in the UK. But how big a problem is it and why are ministers making it illegal?

It could be a scene from a market in Mogadishu. Dozens of Somali men are throwing cardboard boxes at each other across a dusty warehouse floor.

Money is exchanging hands amid all the noise and hustle. In fact, this is happening on an industrial estate near London Heathrow and by Tuesday all this activity will be illegal.

That is because of what is inside the boxes that have just been delivered to this depot.

It is a plant called khat or miraa or - more mystically - "Tea of the Arabs". Users chew the bitter leaves of this natural stimulant. It is supposed to make them more alert and raise energy levels, which is why supporters of khat say it is as harmless as coffee or tea.

'Join the jobless'

At the moment, according to the Advisory Council of the Misuse of Drugs (ACMD), about 2,560 tonnes are imported to the UK every year. The Treasury even benefits from £2.5m per annum in taxes on the khat trade.

From his West London depot, Mahat - who did not want to give his surname - oversees the importing of 7,000 boxes of it a week - fresh off the overnight flight from Nairobi.

Image caption Cafe owners from around the UK come to the west London depot to collect boxes of khat to distribute

"Obviously the ban is going to completely shut down my business," he said. "We will have to join the million jobless around here and look for other jobs."

Around the UK there are also hundreds of khat cafes where men from the Somali, Yemeni and Ethiopian communities go to chew.

Looking at the other end of the supply chain, Kenyan khat farmer FG Machuma is worried about how the ban will hurt 500,000 farmers who cultivate the plant in the Horn of Africa.

"This is going to render our people into destitution including women and children."

Khat - its effects and risks

Image copyright Getty Images

The two main stimulants in khat speed up the user's mind and body, like a less powerful amphetamine.

It makes people happy and talkative but can cause insomnia and temporary confusion.

Chewed for a few hours it leaves users with a feeling of calm, described by some as "blissed out".

The drug could make pre-existing mental health problems worse and it can provoke feelings of anxiety and aggression.

It can also inflame the mouth and damage teeth, and there are concerns about the long-term risk of mouth cancers.

Source: Talk to Frank

'Psychosis'

The estimated £15m a year generated for African economies exporting khat to the UK was one of the reasons MPs on the Home Affairs Select Committee opposed the ban.

In a report last year they argued that "the potential negative effects, both on the diaspora communities who consume khat in the UK, and on the growers who cultivate it in Africa, outweigh any possible benefits".

Image caption Khat farmer FG Machuma says chewing the leaves is no worse than drinking alcohol or smoking

The committee told Home Secretary Theresa May: "Khat has no direct causal link to adverse medical effects. There's no good evidence to suggest a direct link between khat use and psychosis."

And the MPs on the committee were not the only ones with concerns. The government's own advisory council also cautioned against a ban, concerned at the lack of evidence that it harms health or wider society.

The UK was at risk of becoming a base for organised criminals who wanted to smuggle khat to other countries where it was controlled Karen Bradley, Home Office minister

The ACMD concluded: "Beyond contradictory anecdotal statements no credible evidence has been found to show a direct causal relationship between khat and the various harms for which its consumption is claimed to be responsible."

But in an article for the World Health Organisation on Yemen, where an estimated 90% of adult males chew for three to four hours a day, Dr A A Gunaid from Sana'a University has warned: "Khat chewers experience euphoria followed by depression, while people who are genetically predisposed are extremely vulnerable to psychosis."

In the end, the home secretary pushed ahead with plans to make khat illegal.

'Distracting from education'

Data from the NHS in England for 2010/11 shows 112 people starting drug treatment cited past involvement with khat.

In Wales, six referrals have been recorded since 2009 on the Welsh National Database for Substance Misuse.

Karen Bradley, the Home Office minister overseeing the ban, admits hard evidence is difficult to come by, partly because the communities which use the drug are so small.

Image caption Karen Bradley: "This affects a very small community"

So given the lack of definite figures and sketchy medical evidence why does the UK government still want to control it?

"We took the decision based on the strong views of the Somali community, particularly the mums and wives," the minister says.

"They felt that khat was stopping the Somali community from integrating; it was distracting the husbands and sons from getting the education and the jobs that their wives and mothers desperately wanted them to get."

She is also keen to point out that the active component chemicals in khat - cathinone and cathine - are actually already banned in their own right - cathinones were sold as legal highs until 2010 when they were made class B drugs.

Image copyright Getty Images Image caption Khat is mainly grown in Kenya, Ethiopia and Yemen

Liban Noah is a community worker from one of the 32 community groups the government says actively lobbied the Home Office for the ban.

And as the minister points out, Mr Noah - from Hayes, west London - managed to get support from many Somali women who are concerned that men using khat do not engage properly with their families because of their habit.

Suaad Abdiaziz is one of those supporting the ban and she has a blunt message for Somali khat-users in their cafes: "You should be taking care of your children and working - not sitting in a room chewing khat."

Mr Noah also contests the idea that khat does not affect the mental health of those who chew it for hours on end. He insists it does because of the insomnia it triggers.

"They don't eat food, they don't sleep when they abuse khat," he said. "That causes huge mental problems and the evidence is that Somali mental breakdown is increasing."

Al-Shabab warning

The imminent ban will bring the UK into line with much of the EU and the US where khat is already a controlled substance.

Ministers say this was also a deciding factor in the arguments to criminalise it.

"The UK was at risk of becoming a base for organised criminals who wanted to smuggle khat to other countries where it was controlled," said Ms Bradley.

Media playback is unsupported on your device Media caption Vice's Alex Miller examined the potential impact of the ban for BBC Newsnight.

Some security experts have even argued that the East African extremist group al-Shabab has profited from the export and sale of khat.

This was dismissed by the ACMD, which complained it had not been provided with "any evidence of al-Shabab involvement despite repeated requests for this information from a number of national and international official sources".

Inevitably - as with all bans - a black market will emerge and the price of khat for those who buy it in the UK will rise. In America, khat currently sells for 10 times the pre-ban price in UK (it costs on average £3 a bunch).

Back at the west London depot, Mahat may be winding down his own import business to stay on the right side of the law, but he believes others will still find a way to bring it into the UK.

"Yes of course they will smuggle it," he says with certainty. "You will see khat around the UK streets."