Ministers are seeking to win over MPs who want a “meaningful” vote on the terms of the UK’s exit from the EU and its future trading arrangements.
Brexit minister David Jones said MPs would get a say on the final draft Brexit agreement before it was voted upon by the European Parliament.
But he also said the UK would still leave the EU, albeit on different terms, if the deal was rejected.
Labour and some Tories want scope for the UK to renegotiate if necessary.
It is yet to be seen whether this is enough to win over opposition MPs and some Tories who oppose a so-called “take it or leave it” deal and want the Commons to be able to send ministers back to the negotiating table in search of better terms.
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The BBC’s chief political correspondent Vicky Young said many normally loyal Tories were worried about Parliament effectively being put in a position of having to “rubber-stamp” the final deal, but were still likely to fall into line.
However, former chancellor Ken Clarke – the only Tory to vote against kickstarting the Brexit process last week – said Parliament should have the opportunity to shape the final deal, while former SNP leader Alex Salmond said MPs should have a genuine choice without the “Sword of Damocles” hanging over them.
Theresa May had already promised Parliament would get a say on the final deal.
Addressing MPs as they debated a bill authorising the government to begin the formal Brexit process, Brexit minister David Jones said the vote would “cover not only the withdrawal arrangements but also the future relationship with EU”.
The vote, he said, would be on the final draft agreement and would be held before the European Parliament considered the matter.
“This will be a meaningful vote,” he told MPs. “It will be the choice of leaving the EU with a negotiated deal or not.”
And asked what would happen if Parliament rejected the Brexit deal or if there was no agreement with the EU to vote upon, Mr Jones said that in each scenario the UK would still leave the EU but “fall back on other arrangements”.
This would effectively see the UK default to World Trade Organization trade rules, involving potential tariffs on exports and imports.
Opponents of Brexit have said this would cause real damage to British business but supporters say the UK can live with the consequences if necessary as the UK would then be free to negotiate its own trade arrangements.
Mr Jones said the government wanted to avoid a situation in which ministers were sent back to the negotiating table to hammer out a better deal.
This, he said, would be hard given the two-year limit for talks and would also be “the surest way of undermining our negotiating position and delivering a worse deal”.
But Labour’s Chuka Umunna said the choice facing MPs was “unacceptable”, Lib Dem leader Nick Clegg described it as a “symbolic handout” while Green Party leader Caroline Lucas said MPs were being “duped”.
MPs, who overwhelmingly backed the European Union Bill last Wednesday, are currently in the middle of three further days of more detailed debate, with the Commons looking at amendments proposed by MPs.
Labour leader Jeremy Corbyn, who backed the Remain side in last year’s EU referendum, has ordered his MPs to support the government’s bill, whether his party’s amendments are accepted or not.
If passed by Parliament – with the House of Lords due to scrutinise it after the Commons – the bill would allow Prime Minister Theresa May to invoke Article 50 of the Lisbon Treaty, getting divorce talks with the EU under way.
Mr Corbyn argues that it would be undemocratic to ignore the will of the people, as expressed in last June’s EU referendum.
Shadow business secretary Clive Lewis has vowed to oppose the bill unless Labour amendments are passed in the Commons.
Frontbench members of parties are generally expected to resign from their post if they ignore a three-line whip.
Shadow cabinet members Rachael Maskell and Dawn Butler quit shortly before last week’s vote, in order to defy Mr Corbyn’s orders, but MPs backed the bill by a majority of 384.