A national survey has found the majority of Americans are now in favour of legalising #marijuana.

A study by the Pew Research Centre found 52% of people thought the use of the drug should be made legal, with people aged 18 to 32 most in favour.

Even opponents of moves to legalise the drug nationwide – something compared to the end of prohibition of alcohol in the 1930s – admit it is probably now inevitable.

Colorado and Washington state voted to legalise the drug last November but it remains illegal at the federal level, prompting a debate about how police should treat producers and users.

In the Rocky Mountains state of Colorado, growers are preparing for a wave of new customers once authorities have worked out how to implement Amendment 64, the vote to legalise.

At the moment only licensed medical users, carrying what is called the Red Card, can buy #cannabis from dispensaries.

Andy Williams, who owns and runs the Medicine Man dispensary in Denver, is rushing to complete construction work which will expand his growing capacity by a third.

He already has 4,000 #plants, carefully cultivated in high-tech “grow rooms” that look more like a science laboratory than the traditional image of cannabis production.

He has invested hundreds of thousands in industrial-scale growing.

He told Sky News: “It really hasn’t hurt anything. We don’t see a sky rocket in terms of our kids using it, we don’t see lots of people getting into accidents on the highway because of it, we don’t see any negative effects.

“What we are seeing is jobs, taxes, all sorts of good things so let’s just take the curtain off this and say what it is – it is recreational.”

He estimates a boom in sales once Amendment 64 takes effect and anyone over 21 can buy the drug legally.

Already the first Amsterdam-style coffee shops have started to spring up.

Veronica Carpio, who owns the Front Tea and Art Shop and used to run a dispensary, said: “I would say it is time to get over it.

“We have had these biases in our culture for decades and they have impacted peoples lives horribly and negatively. It is time to move past that and evolve.”

Her customers believe any attempt to roll back the new law will fail.

“It is historical, it is trailblazing,” Heidi Perreira told Sky News: “There is no way it can go back.”

But some in Colorado are unwilling to give up the fight.

Douglas County has voted to ban cannabis-related commerce, in effect becoming a dry county.

Jack Hilbert, the county’s commissioner, said the decision was taken to reflect the fact that voters there had consistently rejected legalisation.

He said: “There are too many unanswered questions about the safety of this product.”

Even he accepts there is an inevitability about nationwide legalisation. The profits for businesses and the taxes collected by states will prove hard to resist.