In the UK, most councils have made parks alcohol-free zones. Also, the parks are only nice about 3 months a year. The rest of the time it's damp and miserable.
Uh, citation needed?
Some small parks, cemeteries, kids playgrounds maybe
Every large park in London at least is full of people drinking
There's even a kids playground next to a pub in London fields where I often go drinking with other parents while the kids play
Most of the UK has laws or bylaws at least against antisocial drinking e.g. if you're being a twat, violent, homeless, etc you will be asked to pour it out and leave, in incredibly rare cases I guess you might be fined but probably not.
Just having a beer in public at a picnic with friends is fine and is a national pastime.