The UK could become a hub for smuggling the herbal stimulant khat, European police and politicians have warned.
The Netherlands is the latest country to outlaw the sale of the plant, which is now banned in sixteen EU member states and Norway.
Khat is freely sold in the UK and observers say the UK's isolated stance could make it the main base for Europe's khat trade.
The British government has commissioned a new review of khat use.
Until announcing its ban earlier this month, the Netherlands was similar in its stance to the UK where the East African plant is legally imported, sold and consumed.
In 2005 the UK Home Office commissioned a report by the Advisory Council on the Misuse of Drugs (ACMD) which concluded that "the evidence of harm resulting from khat use is not sufficient to recommend its control."
In the UK, the drug is mainly consumed by people of Somali and Yemeni origin and the ACMD report concluded there was "no evidence of its spread to the general population."
Gerd Leers, Immigration and Integration Minister in the Netherlands, says he already has enough evidence of social harm caused by the drug to support a ban, which will come into force from June this year.
Mark Lancaster, MP for Milton Keynes North, argued that khat should be outlawed in Britain in a speech he made in Parliament earlier this month.
But others say that making khat a controlled drug could lead to further problems.
"What worries me about the Netherlands is that once these legal Somali traders are criminalised and have their livelihood taken away from them - what are they going to do next?" says Axel Klein, an expert witness for the ACMD's 2005 report.
"They have contacts, trading skills, financial acumen so it is very possible that they will start trafficking the khat and then diversify into harder drugs.
"This is our main concern when looking at the UK as well.
"Do we really want to create the opportunity for an organised crime syndicate to start-up from nowhere with long term consequences by banning khat?"
Mr Klein argues that khat is chewed mainly by older men in the Somali diaspora and the practice will die out - rather like snuff has done in the UK.
But British-Somali Muna Hassan is not so sure. She blames khat use for inducing her younger brother's paranoid schizophrenia.
He has lived in the UK since the age of five and had a bright future ahead of him, studying at university, when he then started chewing khat.
"The Somali community has a unified voice on this," she told Radio 4's The Report.
"Those who argue against a ban don't know about the community and they can't see all the damage it is doing to families and individuals. We know," she says.
Eleni Palazidou, a psychiatrist who has worked with the Somali community in east London, agrees.
"For me it is a drug - no two ways about it.
"Every patient that I have seen who chews khat, I have seen them worsening and it is impossible to get their condition under control.
I have no doubt that khat has a major adverse effect on people's mental health and does cause psychological problems," she told The Report.
The Netherlands' ban has been welcomed by Dutch citizens like Dagmar Oudshoorn, mayor of the village of Uithoorn, near Schipol, who says the khat trade has been a blight on her community.
"Four times a week 200 cars arrive with people who want to buy khat and they fight - we had stabbing incidents - and they leave rubbish everywhere.
"We want to refurbish our business area but because of the bad environment we lose investors and customers," she told the BBC.
Neighbouring states, where the drug has long been illegal, have also put pressure on the Dutch government in The Hague because they have seen a sharp increase in khat trafficking from Holland.
For Europe's Nordic countries, much of the khat arrives by truck across the Oresund bridge between Denmark and southern Sweden.
Swedish police estimate that 200 tonnes is smuggled into the country each year, with a street value of 150 euros (£125/$190) a kilo.
After years of lobbying, Swedish MEP Olle Schmidt admits he was pleasantly surprised by the Dutch move to ban khat.
"There is a shift in the Netherlands. They no longer want to be seen as a liberal country where tourists can come to smoke pot and buy drugs.
"Now, of course, khat will come more extensively to the London airports and then be smuggled to the rest of Europe, because you can earn a lot of money with this drug," warns Mr Schmidt.
Stefan Kalman, a senior detective in the Swedish drug squad, says customs officers catch smugglers on the border several times a week.
"The couriers often have accidents because they drive so fast", he says.
"Sometimes they shoot past the border controls without stopping because they are nervous - khat is quite bulky and you cannot conceal it like other drugs."
They are also in a rush because the drug has to be consumed when it is fresh.
Cathinone, one of the psychoactive agents in khat leaves, is highly unstable and loses its potency within three days of harvesting.
With the door slammed shut in Holland, smugglers will turn to the UK despite the longer distances says Detective Kalman.
"With the Eurotunnel you can get from London to Malmo in 15 hours. Britain will become the new hub in Europe that is for certain."
The British government has commissioned a new review of khat use - the date of its publication is still to be confirmed.
By Lucy Ash
BBC Radio 4, The Report