Khat, the herbal stimulant drug is to be banned by the Home Secretary, against the recommendation of the government's official drugs advisory body.
The Advisory Council on the Misuse of Drugs said khat should remain legally available in a report in January, with "insufficient evidence".
But is the security consideration, that khat suppliers use Britain as a transit country for sales across the world, that May is believed to be most concerned about.
Khat is illegal in most of Europe, as well as the US and Canada, but extremely popular with Somalian and Ethiopians. It is a green-leafed shrub which when chewed and mixed with saliva produces a mild amphetamine high.
The ACMD found "no evidence" khat was directly linked to organised crime.
More than 100,000 people of Somali origin live in the UK, according to most estimates. A 2005 Home Office report found more than half of Somali men in the UK used khat, and that almost 80% used more than they did in Somalia.
In an earlier investigation into crime and terror recruiting linked to Khat cafes in London, The Huffington Post UK report found every aspect of the drug, from its production and export to the cafes where it is sold and chewed, has been linked to the al-Shabaab terrorist group in Somalia.
The khat cafes ('mafrishes') where the drug is usually taken are often almost impossible to find unless you know where to look, and are hidden behind locked shop shutters or unmarked doors.
Critics say they are increasingly acting as recruiting stations for the al-Shabaab terrorist network, and many mafrishes are reportedly hostile to outsiders. The Huffington Post UK was advised not to even attempt to enter.
One of the academics who served on the Working Party investigating khat said it was "disappointing" that a ban had been introduced " in contradiction of the scientific advice she has received" adding that "no evidence of any kind that was shown to us would justify a ban."
The University of Warwick's Professor David Anderson, co-author of The Khat Controversy, said the decision was" a great surprise".
"It is astonishing that a government that claims to support evidence-based policy-making should make such a decision, having been unequivocally told by their own scientific committee that there is no evidence to justify any action.
"The impact of this will be to criminalise khat consumers in the UK, all of whom belong to ethnic minority communities, predominantly Yemenis, Ethiopians, Somalis and Kenyans. Khat trading will go underground, joining other illegal drugs trafficking, filling the pockets of organised criminals who will take over supply. The criminals will be rubbing their hands with glee.
"For producers of the plant, predominantly in Kenya and Ethiopia, the countries from which khat has been imported into the UK, there will also be a significant economic impact. In the Meru region of Kenya, khat is these most important cash crop and its income is crucial to the welfare of many rural households."