It would NEVER work in the UK.
Several reasons why.
We are an island, surrounded by countries who have criminalised weed, so we would never be able to import it, our entire supply would have to be "home grown", excuse the pun.
To do it commercially would require paid staff, premises, utility costs, distribution costs, advertising costs. Currently, here in the UK, cannabis farms are worked by slaves, trafficking into the country and are either killed or sold on when no longer needed. Children are exploited to distribute and sell the drug, it's grown in abandoned buildings or cheap rentals, there is very little cost to the dealers. This would not be the case if it were legal, overheads would have to be paid. So the price of a bag of weed would go through the roof. Consequently the value of the "stock" held by producers would mean that 24 hour security was necessary, as well as massive insurance costs.
It would need to be standardised, like alcohol, and licences would have to be issued to people selling it. Those standards would have to be enforced through testing and checks. And only certain strains would be legal. Like alcohol, certain drinks must be a particular proof, otherwise you could kill somebody by selling 70% ABV beer.
It's a plant that anybody can grow. So why would I pay "weedRus" £20 a bag when I could grow it myself for free at home now that it's legal. And I could grow any strain I wanted. Or even, I dunno, sell my cheap weed to my friends for less than they would pay at in the shops. I could be a DRUG DEALER!
Even in countries where it is legal, there is still a massive problem of illegal dealing.
Cannabis psychosis IS very real.
Legalised weed would just be swapping one problem for another.