The British parliament will hold five days of debate on the prime minister's Brexit deal

London (AFP) - British MPs on Tuesday begin debating a highly contentious Brexit deal amid a row over the government’s refusal to publish its legal advice, as a top EU court lawyer said Britain can unilaterally change its mind about leaving the bloc.

May is facing opposition on all sides of the House of Commons to the withdrawal agreement she struck with the European Union last month, and it risks being rejected in a vote on December 11.

The Conservative leader will open the first of five days of debate on Tuesday, insisting her deal is the only option for a smooth Brexit in March.

“This is the deal that delivers for the British people,” May will tell 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.”

However, her speech will be delayed by a dispute over the government’s refusal to publish the full legal advice on the Brexit deal, despite a resolution to that effect passed by MPs last month.

Theresa May has been challenged over Brexit by hardline eurosceptics in her own party

The row, which could see a minister suspended from the Commons, is a reminder of how little control May’s fragile minority government has over MPs ahead of next week’s crucial vote.

May has warned that rejecting her deal could see Britain leaving the EU with no agreement – risking a major recession – or no Brexit at all.

Pro-European MPs pressing for a second referendum with the right to stay in the EU received a boost Tuesday from an opinion issued by a legal adviser to the European Court of Justice (ECJ).

Advocate General Campos Sanchez-Bordona stated that Britain could, if it wanted, stop Brexit without the agreement of other EU countries.

“That possibility continues to exist until the withdrawal agreement is formally concluded,” he said.

Alyn Smith, an MP from the Scottish National Party who was among those who brought the case, said: “We now have a roadmap out of the Brexit shambles.”

- Renegotiate Brexit? -

The vote next week has huge implications for Britain’s future and that of May herself.

The left-wing Labour party, which rejects the deal and has raised the possibility of a second referendum, says it would likely trigger a confidence vote to bring down her government if May loses.

May, who has been constantly challenged by hardline eurosceptics in her own Conservative party, could also face an internal leadership contest.

The 2016 referendum, in which 52 percent of Britons chose to leave the EU, was deeply divisive and there remain strong feelings on both sides.

Brexit timeline, 2016-2020

Lawmakers are just as divided. Although a large majority voted to start the Brexit process, they cannot agree on how it should end.

Hardline Conservative Brexiteers say May’s compromise deal does not represent enough of a break with Brussels.

The Democratic Unionist Party (DUP), the Northern Ireland party propping up May’s government, also objects to special provisions for the province.

Pro- and anti-Brexit demonstrators rallied near parliament

Many of May’s critics want her to go back and renegotiate – some suggest she could do so immediately. Two days after the Brexit vote, she is due in Brussels for an EU summit.

- Parliament in gridlock -

On Monday, pro-European MPs delivered petitions to Downing Street signed by one million people calling for a second vote to resolve the issue.

“It is the only thing you can really do if parliament is in gridlock,” former Conservative minister Justine Greening told AFP.

The EU Withdrawal Agreement covers Britain’s financial settlement, estimated at £39 billion (43.7 billion euros, $49.8 billion), the rights of EU expatriates and plans for a post-Brexit transition period lasting to December 2020.

The transition is intended to give both sides time to strike a new trade and security relationship, as set out in an accompanying political declaration.

If this relationship is not settled by then, the withdrawal agreement provides a “backstop” arrangement that would keep Britain in an EU customs union, with Northern Ireland also following EU rules on regulation of goods.

May insists this is necessary to avoid border checks in Ireland, amid fears of any risk to the fragile peace on the island.

But opponents say this risks tying Britain to the EU for years to come, and with no say in the bloc’s rules, leaving it a “vassal state”.