Britain would be "bonkers" to leave the EU, film maker Michael Moore said as he threw his support behind Jeremy Corbyn becoming Prime Minister.
The American director said it was not his place to tell the British people how to vote, but accused Brexit supporters of throwing tantrums ahead of the referendum later this month.
Michael, 62, in the UK promoting his latest film Where To Invade Next, called Britain "toxic" for considering leaving the EU and electing a Conservative government.
He said: "You're an island, your island is part of a greater world and to want to separate yourselves from that world, it seems a little bonkers to us, but it is your thing."
He added: "Don't you feel you still have something to offer Europe? Be the leaders you have been and are. Get more involved, not pick up our little toys and go home and sit on our little island.
"You saved Europe. Europe today is a large part because of you, the UK. You sacrificed and suffered in the '30s and '40s to save Europe. Why would you want to leave?"
Michael, a long-time supporter of Democratic party presidential candidate Bernie Sanders, called last year's election of Corbyn as Labour leader atonement for electing Tony Blair.
He said: "It's incredible. When I saw that the party here had elected Corbyn, 'I thought 'wow'. Talk about atonement for Blair.
"That's getting back to Labour in its roots."
He added that he wished the late left-wing Labour MP Tony Benn was "still around" to see the possible election of Corbyn as Prime Minister in 2020.
The documentary maker also called on Britons as the "masters" of satire to "bring down" Republican presidential candidate Donald Trump when he visits the UK later this month.
Controversial Trump arrives in the UK on June 24 - the same day Britain will learn the result of the referendum on the EU.
Asked what he thought of the visit, Michael said: "You're actually going to let him in?"
He then added: "I hope satire is what brings Donald Trump down, and you could do a little bit of that while he's here. Because aren't you guys the masters of this? The originators."
Where To Invade Next, which arrives in UK cinemas on Friday, argues for the United States to borrow social and political ideas from countries in Europe and North Africa.
In the film, Michael visits several countries including France and Portugal but not Britain.
He said: "It was a conscious and purposeful decision to not go to the UK, with all due respect. We didn't feel there was anything left to learn here, and you have given up on yourselves to such a degree."