The Green Party will offer voters the chance of a second referendum with the option to remain in the European Union (EU) once the final terms of the Brexit deal have been negotiated, its leader Caroline Lucas will say.

“A democracy worthy of the name must mean people having a real say over the major decisions that affect their lives”, Ms Lucas is expected to tell workers and activists at Space Studios in London, an art studio which benefited from EU funding.

“That’s why the Green Party has consistently said that the referendum should be the start, not the end, of the democratic process. And it’s why today we are announcing our intention to push for remaining in the EU to be an option in a ratification referendum.”

Lucas is expected to add: “Whoever wins this election has a mandate to negotiate on behalf of the British people – but that does not mean that they have a right to impose a final deal. Instead we demand a ratification referendum which gives people the option to remain in the EU if they wish, or to vote back the Government’s deal."

Article 50 states the UK has two years to negotiate its withdrawal, but it is possible Brexit could take even longer, as its terms must be unanimously approved by the 27 remaining member states.

The Greens’ 2017 manifesto will pledge a "ratification referendum" to be held only after the EU has agreed the terms of Brexit.

The party has previously stated its support for a second referendum, but the manifesto will explicitly say for the first time that the ballot paper should include an option to rejoin the European Union if a majority of the electorate are unhappy with the final deal.

Caroline Lucas accuses Theresa May of trying to 'pimp out parliament'

The Liberal Democrats have also said they would like to see a ratification referendum at the end of the negotiation process.

Party leader Tim Farron said their manifesto would confirm his party’s policy that the final say over any Brexit deal struck by Theresa May should rest with “the people in a referendum”.

Speaking to The Independent, Mr Farron said the Liberal Democrats would also give the British people to choice to remain in the European Union.

“Democracy didn’t end on June 23 and the people must have their say over what comes next.”

UK General Election 2017 Show all 47 1 /47 UK General Election 2017 UK General Election 2017 12 June 2017 British Prime Minister Theresa May leaves 10 Downing Street for the 1922 committee on June 12, 2017 in London, England. British Prime Minister Theresa May held her first cabinet meeting with her re-shuffled team today Getty Images UK General Election 2017 12 June 2017 DUP leader Arlene Foster stands alongside deputy leader Nigel Dodds as they hold a press conference at Stormont Castle as the Stormont assembly power sharing negotiations reconvene following the general election on June 12, 2017 in Belfast, Northern Ireland. Discussions between the DUP and the Conservative party are also continuing in the wake of the UK general election as Prime Minister Theresa May looks to form a government with the help of the Democratic Unionist parties ten Westminster seats. 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The Labour leadership say they respect the result of the 2016 referendum, and will not offer voters a second chance to rejoin the EU.

However, Labour MPs Clive Lewis and Rachael Maskell contradicted the party line and authored a joint article in The Guardian on Saturday, calling for a second vote on the final Brexit deal.

“Giving the British people a chance to “seal the deal” with a vote on the final terms of the Brexit negotiations is not asking the same question twice”, the MPs wrote.

“If they really believe their own rhetoric, even Tory Brexiteers should welcome a chance to put their Brexit before the people and get their support."

The Greens’ pledge comes after reports published in the German newspaper Frankfurter Allgemeine Sonntagszeitung said a preliminary meeting between the European Commission President Jean-Claude Juncker and Theresa May was a “disaster”