The Dutch have long been famous for their tolerant attitude to cannabis.
But now they are re-examining their approach, because millions of European "drugs tourists" are heading to the Netherlands to do what they cannot do at home, the BBC's Mike Donkin reports.
The quaint streets of Maastricht are a top attraction for tourists - especially, these days, "drugs tourists".
Mayor Leers: Drive to decriminalise cannabis trade
They flood in across the border from Germany and Belgium, along with the international criminal gangs who operate the drug supply lines.
Maastricht's citizens want an end to this, the city's Mayor Gerd Leers says. So he has called for the Dutch and the rest of Europe to adopt a common "pragmatic approach" to soft drugs.
Mayor Leers has told the Dutch parliament that the licensing system that allows coffee shops to sell 5g of cannabis to each customer should be extended, to allow them to grow their own plants.
"They should have a permit to grow their own cannabis so that they can cut their ties with the criminals," the mayor says. "That way we can control things. At the moment our system is so hypocritical."
Jaap Louwerier, owner of The Fantaisie in Amsterdam, agrees with that. His coffee shop is popular with customers who come to the city for the weekend from France, Britain, Ireland and elsewhere to buy cannabis. "This is all quite legal," he says.
"But it is illegal for me to buy the bigger and bigger stocks of cannabis I need to supply these smokers. And the law says I can only keep up to 500 grammes on my premises, which is not enough. In the coffee shops we call this the 'back-door problem'."
The Dutch have seen a boom in illegal cannabis plantations
In a dim corridor behind the shop, he covertly buys a stash of cannabis from a supplier, while keeping an eye on the door.
"If the police came in now they would confiscate all this," he says. "That's happened once already, and if it happened three times, I'd lose my licence."
Illegal plantations have sprung up across the Netherlands to supply the coffee shops - in outhouses, basements and attics.
What are these secret gardens like? In one old apartment, a bedroom floor is covered with plastic sheeting and earth, and orange lights provide artificial sunlight above a mini-forest of lush green plants.
For many poorer families in the Netherlands, cannabis cultivation has become a tempting way to make some extra cash. There have been prosecutions, but only a handful.
Dutch scientists have warned, however, of the health dangers from this cottage industry.
At a drugs institute in Utrecht, which carries out research for the government, Harald Wychgel hands me samples collected from the coffee shops - fresh hashish and fat, pre-rolled joints.
MP Cisca Joldersma wants tough action to curb drugs tourism
"It's not clear how any of this is produced," he says. "So you don't know how strong it is - whether it's mild or very strong cannabis - or whether pesticides have been used on the plants.
"You cannot be sure what you are smoking. And with drugs it is always safest to know for sure."
Right-wing politicians in the Netherlands say that drugs tourism, and the contradictions this has revealed in the cannabis laws, show that liberalisation has had its day. They oppose the Maastricht mayor's call for coffee shops to be given growers' licences.
"That would only mean more drugs tourists and encourage the criminals," says Christian Democrat MP Cisca Joldersma.
She wants most of the coffee shops to be closed down and a different sort of licence to be issued - an identity card for Dutch cannabis users, so that foreigners would be kept out of the shops that remained.
Amsterdam coffee shop smokers see no immediate threat
"The drugs market is a global market," Mrs Joldersma says. "So we cannot have our liberal policy in isolation."
She says the Netherlands must get tougher on soft drugs. "We want one strong European policy, which the Netherlands has to adopt."
Mayor Leers says that would mean throwing away a drugs policy which has been shown to work, for the sake of uniformity. He wants all of Europe to treat cannabis as tolerantly as the Dutch, eliminating drugs tourism, and has summoned fellow civic leaders from other nations to a conference to tell them the advantages that would bring.
"If you look at the figures you can see that only a small percentage of the youth in the Netherlands is addicted to cannabis. In Germany, Belgium and France the figures are much higher," the mayor says. "So our policy works. It is a good policy."
Back in The Fantaisie, the music and the mood are mellow in the smoke. Erick, a Dutch customer, thinks there is no way his government can put the clock back and criminalise cannabis again.
"If they make it illegal, the coffee shops will just go underground, like in the rest of Europe. I mean people haven't stopped smoking there. They can ban cannabis, but they won't stop people smoking."