British Prime Minister Theresa May has reiterated that a delayed parliamentary vote on her widely maligned Brexit deal will go ahead later this month and warned the UK would enter "uncharted territory" should it be rejected by MPs.

In an interview with the BBC on Sunday, May pledged to set out new measures to address the contentious Northern Irish "backstop" clause in her withdrawal plans in a bid to win over sceptical legislators.

She also promised a greater role for the British Parliament in negotiations over future trade relations with the European Union.

"If the deal is not voted on at this vote that's coming up then we are going to be in uncharted territory and I don't think anybody can say exactly what will happen in terms of the reaction we will see in parliament," May told the BBC.

Parliamentary opposition

The UK is poised to leave the EU on March 29, two years after it triggered Article 50, the exit clause in the EU's constitution, and kick-started arduous negotiations with European leaders over a divorce deal.

Last month, May pulled a vote on the brokered withdrawal agreement, settled on in November after more than a year of back-and-forth negotiations between London and Brussels, acknowledging it would have been roundly rejected by the UK's lower chamber House of Commons.

She later announced the vote would go forward in the week beginning January 14.

181214120018250

But parliamentary opposition to her deal remains fierce, with the main sticking point being the safety net "backstop" measure - which would guarantee no hard border is erected on the island of Ireland in the event that post-Brexit trade negotiations between the UK and the bloc prove unsuccessful.

Critics of the backstop, which proposes that the whole of the UK, including Northern Ireland, remain in a customs union with the EU "unless and until" the bloc agrees there is no prospect of a return to a hard border, argue it could tie the UK into the EU's orbit indefinitely.

In an effort to assuage MPs concerns, May has lobbied her European counterparts and officials in Brussels to make concessions on the clause.

The EU, for its part, has insisted that the withdrawal agreement cannot be renegotiated but has made clear the backstop is meant only as a temporary measure of last resort.

DUP digs its heels in

The Northern Irish Democratic Unionist Party (DUP), which May's ruling Conservative Party relies on to command a majority in parliament, has urged the British leader to stand firm in demanding that the EU changes its "poison" backstop provision on Ireland's post-Brexit border, however.

"The backstop remains the poison which makes any vote for the Withdrawal Agreement so toxic," DUP Deputy Leader Nigel Dodds said in a statement on Sunday.

"The coming days will show if this government is made of the right stuff," he added.

The main opposition Labour Party has also pledged to vote down May's deal in parliament and threatened to initiate a no-confidence vote in her leadership should MPs refuse to back her plan.

181208084355355

Analysts said May's comments to the BBC did little to conceal the fact the British leader has no "gamechanger" amendments to the proposed withdrawal agreement capable of swinging the parliamentary arithmetic in her favour.

"We are pretty much where we were before Christmas, with the proviso that there's less time left. I don't see how the deal passes at the moment ... the interesting thing will be how much it loses by at the first attempt," Anand Menon, a professor of European politics and foreign affairs at King's College London, told Al Jazeera.

"There are some MPs who are looking for an excuse to back the deal and so, something tokenistic and declaratory from the EU on the backstop clause would work for them, but I don't understand how that would work for the DUP, and that's where the action is," he added.

"Peeling off five of 10 Conservative Party MPs is neither here nor there, but if you get the DUP in line, May will give lots of parliamentarians an excuse to say, 'Well, OK, if they're happy with it I can't really justify going around moaning about the Irish backstop.'"

No-deal departure fears

Amid the ongoing uncertainty surrounding Britain's high-drama Brexit process, fears that the country could exit the 28-member EU bloc without a deal on the terms of its departure have continued to escalate.

181218142414510

The UK's central bank has warned that Britain's gross domestic product could shrink by up to eight percent in such a scenario. The government, for its part, has forecast a potential economic slump of more than nine percent in the wake of a no-deal Brexit.

In a letter published by UK newspaper the Mail on Sunday, May warned critics of her departure plan risk damaging Britain's democracy and weakening its economy by opposing her deal.

She also alleged her deal was the only one that respects the UK's 2016 referendum result, in which 52 percent of Britons voted to leave the EU.

Growing calls for referendum rerun

But a new survey published by polling firm YouGov on Sunday suggested more Britons now want to remain a member of the bloc than leave it, however.

181201182945771

According to the research, which was commissioned by pro-second referendum campaign group the People's Vote, 46 percent of voters would opt to remain while 39 percent would vote to leave in the event of a rerun of the 2016 ballot.

When the undecided and those who refused to answer were removed from the sample, the split was 54-46 in favour of remaining.

The survey of more than 25,000 voters also showed that 41 percent of Britons thought the final decision about Brexit should be made by a new public vote versus 36 percent who believe it should be up to parliament.

Removing those who are undecided, the split was 53 percent in favour of another referendum and 47 percent against.

Menon, however, argued the prospect of a second referendum being held remained slim.

"It's very hard to achieve - there isn't a majority in parliament for it … [and] it would require a significant extension of Article 50," Menon said.

"It's also impossible to say whether public opinion is in favour of a second referendum or not because answers to that question have varied basically as a function of the question that's being asked," he added.

"The polls split very clearly depending on the question you ask."

Additional reporting by David Child: @DavidChild90