Members of Britain's Parliament kicked off five days of debate on Tuesday to rake over the Brexit deal negotiated by Prime Minister Theresa May.

At the conclusion of the discussions, which are likely to be feisty, MPs will vote on whether or not to accept the agreement that sets out how the United Kingdom will interact with the European Union after its withdrawal from the bloc at the end of March. The vote is set for Tuesday, Dec 11.

May's deal is unpopular among many MPs and is likely to be defeated, according to current projections, which would create more uncertainty and could see May unseated as prime minister, a general election, and possibly a reopening of negotiations with the EU, as well as potentially unleash a so-called people's vote during which the UK's electorate would again be asked whether they want to leave the EU.

But before the debate started, May's cabinet faced criticism for refusing to release in full the advice of the government's lawyers on the legality of the proposed deal and its long-term implications.

The government's chief legal adviser, Attorney General Geoffrey Cox, published an overview of his advice on Monday but that was not enough to satisfy many MPs who said a binding Commons vote on the issue meant the advice should have been published in full.

Cox told MPs on Monday his advice contained no bombshells and should remain private.

"There is nothing to see here," he said. But the opposition Labour Party's Brexit spokesperson, Keir Starmer, told the BBC he wanted transparency.

"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," Starmer said.

Labour is calling for the immediate publication of the advice and is being backed by minor parties, including the Liberal Democrats, the Scottish National Party, the Democratic Unionist Party, Plaid Cymru, and the Green Party.

Commons Speaker John Bercow, who enforces Parliament's rules, said on Monday the critics had an "arguable case" that a contempt of Parliament had been committed and the matter was referred to Parliament's Privileges Committee.

May intended to kick off Tuesday's debate by insisting Britain could have a better future outside the EU, and noted that her deal allows the country to take back control of its borders, its laws, and its currency.

Downing Street said she would also say: "The British people want us to get on with a deal that honors the referendum and allows us to come together again as a country, whichever way we voted."

But her proposed deal satisfies neither hardline Brexiteers who want to sever the nation's ties with the EU, nor Remainers who want Britain and the EU to be closely bonded. It is also controversial because of its so-called backstop provision on the border between Northern Ireland, which is part of the UK and will leave the EU, and the Republic of Ireland, which remains a member. The backstop tries to avoid a hard border between them if no future trade deal is agreed by binding the UK to the EU's customs rules. Critics say this means the UK could be effectively be trapped indefinitely within the EU while having no role in its governance.

If May's deal is defeated in Parliament, the push for a second referendum is likely to intensify but Cabinet member Michael Gove, the environment secretary, warned on Sunday that May's critics should think twice before trying to maneuver her into holding a second poll. He said it could backfire on Remainers and deliver even more support for Brexit than the last poll in 2016.