Prime Minister Theresa May is preparing to sell her Brexit deal as she opens five days of debate in the Commons.
The debate is due to last eight hours each day and to begin mid-afternoon. MPs will vote next Tuesday evening.
The deal negotiated by the UK and the EU has to be backed by a majority MPs if it is to come into force.
But ahead of the debate, ministers face a contempt-of-Parliament challenge over their decision not to release the full legal advice on her Brexit deal.
The legal advice row
The government’s chief legal adviser, Attorney General Geoffrey Cox, published an overview of his legal advice on Monday.
Opposition parties say that by limiting the information released, ministers ignored a binding Commons vote demanding they release the full advice.
Labour’s shadow Brexit secretary, Sir Keir Starmer, said: "It’s about parliamentary democracy and guaranteeing that MPs have the information they need to know – precisely what the government has negotiated with the European Union."
Sir Keir signed a motion demanding immediate publication of the full and final advice, along with senior MPs from the Liberal Democrats, the SNP, the Democratic Unionist Party, Plaid Cymru and the Green Party.
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Commons Speaker John Bercow said late on Monday there was an "arguable case" that a contempt of Parliament had been committed.
However, the government then tabled an amendment to have the issue referred to MPs on the Privileges Committee to investigate whether its response fulfils all its obligations, taking into account any relevant past cases.
BBC political correspondent Iain Watson said any defeat over the legal advice would be likely to come as "an unwelcome distraction rather than a disaster" for the prime minister.
"While ultimately a parliamentary committee could decide to reprimand or suspend ministers, it’s highly likely no sanction would be applied before next week’s crucial vote on the Brexit deal," he said.
The crunch debate on Brexit deal
Opening what looks set to be the defining moment for her version of Brexit, Theresa May is expected to say the UK is on course for a "better future outside the EU" and that her deal "takes back control of our borders, laws and money".
However, the prime minister faces opposition from MPs on all sides – including both the Leave and Remain wings of her own party – who argue that better deals could be available or that the public should have the final say in a referendum.
Many believe her deal is flawed because of a "backstop" that could keep the UK tied to EU customs rules in the event no future trade deal can be agreed. Some believe only the full legal advice will shed light on this.
Cox: Brexit backstop a ‘calculated risk’ for UK
On Monday, when he published an overview of his legal advice, the attorney general said releasing the advice in full would break a longstanding convention keeping legal advice to ministers confidential, but insisted there was no cover-up, telling MPs: "There is nothing to see here."
Mr Cox accepted the backstop – designed to protect Northern Ireland’s peace process by preventing the return of customs posts and checkpoints on the Irish border – could leave the UK "indefinitely committed" to EU customs rules if Brexit trade talks broke down.
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The arrangement, which would apply to the entire UK, is supposed to be temporary. However, neither side could withdraw from it without the other’s consent.
Mr Cox accepted that signing up to it was a "calculated risk" but added: "I do not believe we will be trapped in it permanently."
How the debate will work
MPs will debate different aspects of the agreement, signed last month with EU leaders after months of wrangling, before voting on 11 December,
Senior ministers are being lined up to make the case for it.
- The first day of debate will be closed by Brexit Secretary Stephen Barclay
- The second day, on Wednesday, will focus on security, with Home Secretary Sajid Javid opening the debate and Foreign Secretary Jeremy Hunt closing it
- Thursday’s debate will be on the economy, with Chancellor Philip Hammond opening it and International Trade Secretary Liam Fox winding up
Further details have still to be announced but Mrs May will kick off proceedings by telling MPs: "The British people want us to get on with a deal that honours the referendum and allows us to come together again as a country, whichever way we voted."
Brexit vote: Will MPs back deal in Commons?
Brexit vote: Will MPs back deal in Commons?
Mrs May will argue her Brexit deal delivers on her commitments to end free movement and the jurisdiction of the European Court of Justice.
It will leave Britain "as a globally trading nation, in charge of our own destiny and seizing the opportunities of trade with some of the fastest-growing and most dynamic economies across the world", she will add.
Mrs May will say future trade talks with Brussels will also ultimately result in "a new free-trade area with no tariffs, fees, quantitative restrictions or rules-of-origin checks – an unprecedented economic relationship that no other major economy has".
Labour is threatening a vote of no confidence in the government as part of a move to trigger a general election, if Mrs May is defeated on 11 December.
The party is in favour of Brexit but against Mrs May’s deal, which it argues will harm industry and cost jobs. It wants to delay Brexit to negotiate a better deal with Brussels.