LONDON (Reuters) - Eight out of 10 grassroots members of Britain’s opposition Labour Party want a referendum on the terms of the country’s exit from the European Union, according to a survey published on Thursday.

An EU flag and Union flag are seen flying together during an anti-Brexit protest near the Houses of Parliament in London, Britain, December 8, 2017. REUTERS/Toby Melville

That is at odds with Labour leader Jeremy Corbyn’s official policy which calls for parliament, not the public, to have the final say on the terms of the deal.

It indicates a strong desire among the party’s rank and file members for a chance to demand a rethink on Brexit, or even overturn the outcome of the June 2016 vote to leave the EU.

Eighteen months after voting 52 to 48 percent to withdraw from the EU, Britons remain deeply divided over leaving a bloc which has defined much of the country’s laws, trade policy and international outlook over more than four decades of membership.

Theresa May’s Conservative minority government has dismissed the idea of a second referendum.

But ministers have already been forced to give parliament a greater say in the Brexit process than they initially wanted to after members of May’s own party rebelled on the issue in December.

Thursday’s survey of attitudes within Britain’s main political parties showed 49 percent of Labour members definitely wanted a second referendum on the exit deal and a further 29 percent said they were more in favour of the idea than against it.

The poll of more than 4,000 members of political parties was conducted shortly after last June’s national election as part of a three-year academic project by the Mile End Institute at Queen Mary University of London to discover more about people who belong to political parties.

It showed even higher demand for a second vote on Brexit among members of the Liberal Democrats and the Scottish National Party. By contrast, only 14 percent of Conservative Party members wanted a referendum on the exit deal.

Opinion polls measuring the views of the wider electorate show similar divisions over Brexit. In December, one survey showed 50 percent of voters supported a second referendum while 34 percent did not.

Labour’s official stance on Brexit gained new significance after last year’s general election saw them perform better than expected.

That helped reopen a national debate about Brexit, depriving May of the unequivocal mandate she was seeking for her plan to take Britain out of the EU, its single market and the bloc’s customs union.