To answer some of the questions above in more detail, about why Corbyn is an idiot.
His opposition to the EU comes from an anti-neoliberal critique of the EU. Fair enough: he wants better worker protections, less rampant free market capitalism, etc. All good things and all traditional socialist positions. The EU is pro neoliberalism, so it makes sense to be against the EU if you are anti-neoliberalism. This has long been a Leftist critique, across Europe.
But the idea that the UK leaving the EU will bring about an alternative socialist future in the UK is preposterous. It's just so far from anything realistic, it make me really doubt Corbyn's intelligence. Brexit is going to result in neoliberalism and free trade on steroids! That's the whole point of why the Tories and people like Farage support it, because free market economics mean the rich get richer! Jeremy Corbyn acting all shocked and surprised that Brexit might lead to fewer regulations and protections for workers, rather than more, is either hypocrisy or stupidity.
Greece had a good reason to leave the EU: free market economics following the 2008 crash decimated its economy and society. Greece has a strong and recent socialist tradition in politics. If Greece had left the EU, there was a realistic chance that they would have embraced an alternative economic situation that would led to better worker rights and a fairer society.
But the UK is not Greece. Greece -- which was being screwed over by richer EU countries like France, Germany and (yes) the UK - had a reason to complain; the UK really didn't. The UK has always been one of the beneficiaries of the EU's neoliberalism. (British people today complaining about the EU is as illogical as 19th Century Victorian mill owners in Lancashire complaining that the slaves picking cotton on American plantations are oppressing them. Rich countries like the UK benefit from countries like Greece getting screwed over.)
If Corbyn wanted to do something about the rampant inequalities wrought by neoliberal, free market economics, he would have supported changing the EU to make it fairer for poorer countries like Greece. The UK is (was) one of the richer countries in the EU. The fact that there is vast amounts of poverty in the UK is due to the unequal distribution of all that money -- not that there isn't any of it. The UK could have used its economic and political clout to bring about change for everyone in Europe, the UK included. But instead, he thought that somehow going it alone, reducing our global power significantly, and opening us up to total exploitation by the US (esp under the current lunatic Trump), was going to result in.... Well who knows. A socialist revolution? A workers uprising, where the people of Britain rise up and sing the internationale while storming the means of production?
I can't even.
Corbyn believes that Brexit is going to result in more equal distribution, better worker protections, and more regulation of capitalism. The only conclusion I can come to is that the man is just a naive fool.