Jeremy Corbyn has ruled out ever sharing a stage with Prime Minister David Cameron on Europe, saying the two have "opposite" agendas.
Both Mr Corbyn and Mr Cameron are campaigning for Britain to remain in the EU, but the two have different views on what the Union should look like.
Speaking on ITV's The Agenda, the Labour leader, criticsed Mr Cameron's vision of a "free market Europe".
Jeremy Corbyn speaks to The Agenda:
Asked if he could ever see himself supporting Mr Cameron on EU membership, given that they both believe the UK should remain in the Union, he replied:
No. We are not on the same side of the argument. He wants a free market Europe. He has negotiated what he believes is some kind of deal over welfare and the ever closer union, which is apparently legally questionable, according to Michael Gove. I want to see a Europe that is about protecting our environment and ensuring we have sustainable industries across Europe such as the steel industry and high levels of jobs and social protection across Europe. His agenda is the very opposite.
Helena Morrissey, CEO of Newton Investment Management, who was also on the show, said while she appluded Mr Corbyn's vision it seemed an unlikely direction for the EU to take.
"I would love to see what Jeremy is setting out but I think it is fantasy," she said.
On leaving Europe she added: "There is uncertainty if we stay or if we go. I'm not arguing for a slamming of the door and flouncing out but for a conscious uncoupling."
Also on The Agenda tonight:
On Damian McBride's employment by Labour's Emily Thornberry
He's a sinner who has repented. It doesn't mean what he did was OK. It does mean that he like everybody else will work very hard to make sure that we have had proper debate.
On the migrant crisis
There has to be an agreement all across Europe that they all take a proportion of them. The problem is that the degree of inward-looking politics that's going on has mean that Greece is making a huge effort, Italy is making a huge effort and Germany is making a huge effort. Every other country is putting barbed wire entanglements along their borders to keep desperate people out ... Surely in the 21st century the least we can do is reach out and try and help these people in some way, by the political solution in Syria, by the support for what the Greek government is trying to do and take a proportion all across Europe.
On the PM's comment that his mother would criticise Mr Corybn's dress sense
I've never had the pleasure of meeting his [David Cameron's] mother so I have no idea what she would say - my mother gave lots of advice and she said stand up for what you believe in.