The veteran Socialist told the BBC he couldn’t foresee a situation in which Labour, by far the largest opposition party in the U.K., would campaign for a so-called ‘Brexit’ under his leadership. That’s a softening in the position of a man who has in the past denounced the E.U. for hollowing out workers’ rights in its pursuit of free trade deals, exposing them to low-cost competition from places such as China.

Prime Minister David Cameron has promised a referendum on the issue by the end of next year, by which time he hopes to have renegotiated the U.K.’s membership of the bloc on more favorable terms.

Opposition to the E.U. is concentrated in the right wing of Cameron’s ruling Conservative Party and the avowedly anti-immigrant U.K. Independence Party, UKIP, which took 12.7% of the vote at the General Election in May but which only won one seat in parliament. Analysts had feared that Corbyn’s election as Labour leader at the weekend would add a much broader third pillar of support for the pro-‘Brexit’ camp.

Corbyn, who has appointed the pro-E.U. as his foreign policy spokesman, said his party’s position towards the E.U. was “developing”.

“We are having discussions to sort this question out. Basically, on the question of Europe, I want to see a social Europe, a cohesive Europe, a coherent Europe, not a free market Europe,” Corbyn said.

The U.K.’s often stormy relationship with the rest of the E.U. is being sorely tested again by the current migrant crisis. Cameron has used the country’s “opt-out” of certain E.U. arrangements to avoid being included in an E.U. plan to redistribute up to 160,000 migrants across the region in an effort to take the pressure of key chokepoints such as Hungary, Greece and Italy. Senior German politicians have accused it of not pulling its weight.

Cameron has agreed to accept a limited number of refugees from camps bordering Syria over the next four years, but is fearful of letting the crisis turn next year’s referendum into a de facto vote on immigration.