LONDON (Reuters) – The European Union’s top legal adviser said on Tuesday Britain had the right to withdraw its Brexit notice, opening a new front in a battle over Prime Minister Theresa May’s plans to leave the EU, which could be rejected in parliament next week.

The advice from the European Court of Justice’s advocate general will embolden supporters of EU membership in Britain’s parliament on the first of five days of debate on May’s plans to keep close economic ties with the bloc after leaving in March.

May faces a daunting struggle to secure parliament’s approval in the key vote on Dec. 11 after her plan was criticized by Brexit supporters and opponents alike.

The strength of that opposition was clear on Monday, when six parties, including her nominal allies in Northern Ireland’s Democratic Unionist Party, won the right to press an attempt to hold the government in contempt of parliament.

But May is pressing on nonetheless.

“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,” she will tell lawmakers on Tuesday, according to excerpts of her speech.

“This is the deal that delivers for the British people.”

If, against the odds, she wins the vote, Britain will leave the EU on March 29 under terms negotiated with Brussels – the UK’s biggest shift in trade and foreign policy for more than 40 years.

Sterling jumped after the ECJ advocate general’s advice was published, on hopes that it would make a disorderly “no-deal” Brexit next March less likely. [GBP/]

If she loses, May could call for a second vote on the deal. But defeat would increase the chances of Britain leaving without a deal – a prospect that could mean chaos for Britain’s economy and businesses – and put May under fierce pressure to resign.

SECOND REFERENDUM?

Defeat could also make it more likely that Britain will hold a second referendum on exiting the EU – which would almost certainly require it at least to defer its departure – three years after voting narrowly to leave.

May, 62, has toured Britain, spent hours being grilled in parliament and invited lawmakers to her Downing Street residence to try to win over her many critics.

But the deal, sealed in Brussels last month, has united critics at both ends of the political spectrum: eurosceptics say it will make Britain a vassal state while EU supporters – expressing the same idea with different language – say it will become a “rule-taker”, not a rule-maker.

The DUP, which props up May’s government, has rejected the deal and opposition parties say they cannot back it.

Few in the House of Commons, the lower house of parliament, seemed to have been won over on Monday. Her former Brexit minister David Davis said flatly: “This is not Brexit.”

Opposition parties and the DUP will also press on Tuesday for her government to be found in contempt of parliament for failing to publish in full the legal advice on Brexit that it commissioned.

DIVIDED KINGDOM

More than two years after Britain voted to leave the EU, the testy debates that shaped the referendum have increased, deeply dividing the country and increasing uncertainty over its future, which has unsettled markets and businesses.

May hopes that if she forces her deal through parliament, firms that have put off investment decisions and made contingency plans for fear of trade drying up will be able to move forward again.

She says her deal will offer close economic ties with the EU, enable Britain to trade freely with the rest of the world while meeting the demands of voters to end free movement, and reduce immigration into Britain.

But the compromise deal, which ministers openly say is not perfect, has done little more than strengthen opposition at the hardline edges of the debate.

Brexit supporters have vowed to vote down the deal and threatened to bring May down. Pro-EU lawmakers have also said they will vote against it, and the main opposition Labour Party says it will also try to unseat her.

During the five-day debate, the strength of the opposition should become clear when lawmakers make speeches or try to amend, or change, May’s motion to approve the deal – to try to alter or delay Brexit, or derail it altogether.

Labour has already submitted an amendment designed to ensure that the government cannot, under any circumstances, leave the EU without an exit agreement, and must consider all alternatives to doing so.

Pro-EU lawmakers have also put forward another amendment to block the deal and to rule out a no-deal Brexit.

But her team is sticking to the script.

“This deal … is the best way, I firmly believe, of ensuring that we leave the European Union on March 29,” Attorney General Geoffrey Cox told parliament on Monday.

“This is the deal that will ensure that happening in an orderly way, with legal certainty.”