European Diary/ Jamie Smyth: The pungent smell of marijuana hangs in the air on Kleine Gracht street in Maastricht. A group of German teenagers are sharing a joint as they take a Sunday afternoon stroll through the Dutch city. A few metres further on and two men are sitting in their Belgian-registered car smoking a pipe, the plumes of smoke curling through the open window of their Volkswagen.
These are the drug tourists: the thousands of people who travel to Maastricht's 16 legally registered coffee shops every day to buy small bags of hashish and marijuana.
"The trade is best on a public holiday or a Sunday," explains Erik, doorman at the Kosbor coffee shop on Kleine Gracht, which is heaving with people on a bright sunny afternoon. "People come from all over to smoke - from France, Germany, Belgium."
Scrawled in chalk on a blackboard above the in-house dealer is a menu. Afghan at €3 a gramme, black Bombay at €8 and ketama at €2.50 are on sale to customers willing to travel hundreds of kilometres to feed a habit.
For the scores of people queuing up at the Kosbor - most speaking French or German - the Netherlands' liberal drugs policy has clearly created a boom in cross-border trade. But it is a trade that Maastricht's mayor, Geer Leers, could do without.
Alarmed at the volume of "spaced out" young people wandering through the city centre, Mr Leers recently announced plans to move seven of the coffee shops a few kilometres out of town to locations along the border with Belgium and Germany.
Mr Leers is calling the scheme "coffee corner". Locals in the border area are rather less enthusiastic, describing the plan as creating "cannabis boulevards".
Maastricht's border scheme has also alarmed and angered the Belgian authorities.
"I have a good understanding with Mayor Leers, except when it comes to soft drugs," says Alex Vangronsveld, mayor of Lanaken, a Belgian town on the border with Maastricht. "We in Lanaken maintain a zero-tolerance policy. The dispersal plan is not acceptable to us, as Maastricht already has 4,500 drug tourists a day."
Even Belgian prime minister Guy Verhofstadt, a staunch European who promotes the idea of a federal EU, has become embroiled in the affair, sending a letter to his Dutch counterpart, Jan Peter Balkenende, urging him to "respect the principles of good neighbourliness between our countries" and Belgium's zero-tolerance policy on drugs.
Local officials in Maastricht have hit back in the press, accusing the Belgian government of hypocrisy since last year it took the decision to decriminalise the possession of small amounts (3g) of cannabis. If it is legal for Belgians to carry drugs but not buy them, isn't it likely they will travel to cities such as Maastricht to purchase their supplies of marijuana and cannabis? The Belgians need to tackle their drugs problem rather than blame the Netherlands, Dutch officials say.
In an attempt to step up the pressure on the Maastricht authorities, Belgian MEP Ivo Belet asked the European Commission if it could intervene in the drugs dispute. He cited an article of the Schengen Agreement, which deals with measures to combat crime and illicit drug trafficking, as a possible basis for action.
But after analysing the legal basis of the cross-border agreement and the relevant European treaties, justice commissioner Franco Frattini said the decision by Maastricht was not in contravention of the treaties. He also cited the "even closer" co-operation between the Belgian and Dutch police on cracking down on drug trafficking between the two states as evidence that the Netherlands was complying with EU drugs policy.
The EU's inability to intervene in this policy area is good news for Gary, a 70-year old pensioner living in Maastricht, who supports the mayor's relocation plan.
"When you go to church, before the service there are sometimes people begging for money, and there is crime. Many people come from France, Germany and Belgium and the coffee shops are open all the time. The ones on the riverboats even stay open when the river is flooded," says Gary, referring to the Smokey and Mississippi coffee houses in Maastricht, a city probably best known for the EU treaty signed there in 1992 that introduced co-operation in law enforcement and criminal justice matters.
But the Netherlands' unique policy on soft drugs graphically illustrates the difficulties EU states encounter when seeking to co-ordinate action in issues related to justice - an area that the commission is now targeting for closer integration.
For example, this month the Dutch threatened to torpedo a landmark deal on the European evidence warrant over fears that it could lead to a deluge of applications for the transfer of evidence from the Netherlands to support drugs cases in other EU states.
In the end a compromise was negotiated and the agreement was signed, but further EU integration in justice matters is likely to prove controversial as the dispute over Maastricht's coffee house relocation plan has illustrated in recent weeks.