This was covered in the early 20th century by some other laws, but in 1961, the Single Convention on Narcotic Drugs was established by the UN and as of May 2013, the Single Convention has 184 state parties. The Holy See plus all members of the UN are state parties, with the exception of Afghanistan, Chad, East Timor, Equatorial Guinea, Kiribati, Nauru, Samoa, South Sudan, Tuvalu, and Vanuatu.
The coca leaf is listed on Schedule I of the 1961 Single Convention together with cocaine and heroin.
The Convention determined that "The Parties shall so far as possible
enforce the uprooting of all coca bushes which grow wild. They shall
destroy the coca bushes if illegally cultivated" (Article 26), and
that, "Coca leaf chewing must be abolished within twenty-five years
from the coming into force of this Convention" (Article 49, 2.e).
The historic rationale for international prohibition of coca leaf in
the 1961 Single Convention comes from "The Commission of Enquiry on
the Coca Leaf study" published in 1950. It was requested of the United
Nations by the permanent representative of Peru, and was prepared by a
commission that visited Bolivia and Peru briefly in 1949 to
"investigate the effects of chewing the coca leaf and the
possibilities of limiting its production and controlling its
distribution." It concluded that the effects of chewing coca leaves
were negative, even though chewing coca was defined as a habit, not an
Peru and Bolivia, however, have made an amendment, which you can read further about on that page, which is how you're able to have it there. There are some other exceptions supported by some countries, but basically - in Europe - no, it's not permitted...yet.