Theresa May has offered to give MPs a vote on whether to hold a second EU referendum as part of a package of measures she repeatedly called a "new deal" to implement Brexit.
In a dramatic move, the prime minister said the Withdrawal Agreement Bill will include a requirement for the Commons to vote on calls for a so-called "people's vote".
She vowed that if parliament backs the move, the government will make time available for the legislation required for a second referendum to be passed.
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May also unveiled a package of measures she called a "new deal" aimed at trying to win over both Labour MPs and Tory eurosceptics to finally back the bill when they vote on it next month.
On customs – the main bone of contention during the fruitless six weeks of talks between the government and Labour – the PM said parliament would get to decide how to break the impasse.
Other measures included guarantees to match EU standards on workers' rights and the environment, as well as a vow to put the government under a legal obligation to find "alternative arrangements" to the controversial Irish backstop before the end of 2020.
But it was her pledge on a second referendum that could prove to be the most controversial element of the WAB.
Speaking in central London, May said she recognised "the genuine and sincere strength of feeling across the House on this important issue".
“The government will therefore include in the Withdrawal Agreement Bill at introduction a requirement to vote on whether to hold a second referendum," she said.
"This must take place before the withdrawal agreement can be ratified. And if the House of Commons were to vote for a referendum, it would be requiring the government to make provisions for such a referendum – including legislation if it wanted to ratify the withdrawal agreement.
"So to those MPs who want a second referendum to confirm the deal: you need a deal and therefore a Withdrawal Agreement Bill to make it happen. So let it have its second reading and then make your case to parliament."
In an analysis of the plans, the Institute for Government noted that May had "never previously offered a vote on a confirmatory referendum". “This introduces a potential two-stage process,” said the analysis.
May’s pledge to introduce a legal duty to reflect any changes made by parliament to the political declaration of the withdrawal agreement was also a new provision, it said.
“To do that, the UK would need to go back to Brussels to agree them with the EU.
“It’s far from clear these proposals would be acceptable to the EU, in part or in full, so there’s no guarantee those changes could be made. MPs may request a further vote on changes to the political declaration.”
Other elements of May’s speech were new or beefed up promises, while others were a reiteration of pledges already made, the IfG said.
The proposed legal obligation to conclude work on alternative arrangements to replace the Irish backstop – which is intended to maintain an open border on the island of Ireland – by December 2020 in order to ensure the backstop provisions are not triggered is new, although the substance of the drive for arrangements is not.
May also reiterated that the Northern Irish Assembly and Executive will have to give their consent on a cross-community basis to new regulations.
And plans for government to set out in law that the House of Commons will approve the UK’s objectives for the negotiations on the UK’s future relationship with the EU and approve the treaties governing that relationship were also not new, the IfG said.
However, action to protect workers’ rights through a new Workers’ Rights Bill could go further than previous pledges of “non-regression” from EU standards, dependent on the details of the bill.
Pledges to seek "as close to frictionless trade in goods with the EU as possible while outside the single market and ending free movement” and keep up to date with EU rules for goods and agri-food products have also been set out previously, according to the IfG.
May warned that if MPs rejected her attempts to find "common ground" between the rival Brexit factions, the UK could end up staying in the EU.
"There will opportunities throughout the Bill for MPs on all sides to have their say," she said. "But I say with conviction to every MP of every party – I have compromised. Now I ask you to compromise too.
“We have been given a clear instruction by the people we are supposed to represent. So help me find a way to honour that instruction, move our country and our politics forward, and build the better future that all of us want to see."