The wave of negative sentiment felt in Northern Ireland in the wake of Prime Minister Boris Johnson's revised Brexit deal cannot be "underestimated," a British lawmaker told CNBC on Sunday night U.K. time. "I think you can't underestimate the anger, frustration and the betrayal that many many people feel ... in northern Ireland," said Jim Shannon of Northern Ireland's Democratic Unionist Party (DUP), who's an MP for Strangford, a constituency in the province. The border between the U.K.'s Northern Ireland and the Republic of Ireland — a 310-mile frontier set to represent the only land border between the U.K. and the European Union from Oct. 31 — has proven to be one of the biggest hurdles to a Brexit deal.

Traffic crosses the border into Northern Ireland from the Irish Republic alongside a Brexit Border poster on the Dublin road Co Armagh border, between Newry in Northern Ireland and Dundalk in the Irish Republic, on December 1, 2017. PAUL FAITH | AFP | Getty Images

Initially, the so-called Irish backstop required Northern Ireland to be kept very closely aligned to EU customs laws in order to remove the need for physical infrastructure on the Irish border post-Brexit.

We will feel like we will be second class citizens ... whenever they decide to bring in laws and legislation on tariffs and all the other things, we will be subject not to Westminster ... but subject to the EU. Jim Shannon Democratic Unionist Party

But it proved to be very unpopular among pro-Brexit supporters and the DUP who did not want Northern Ireland to be separated from the rest of the U.K.

'Second class citizens'

Johnson's revised deal — approved by the European bloc last Thursday — meant that Northern Ireland would remain part of the U.K.'s customs territory and be the entry point into the EU's single market. But it would still have to apply certain EU rules, including on farm products. That revised deal, however, was opposed by pro-British politicians. Unionist politicians, who are loyal to the union of Northern Ireland and Britain, are concerned that a different customs and tax regime could weaken Northern Ireland's place in the U.K., according to a Reuters report. "We will feel like we will be second class citizens ... whenever they decide to bring in laws and legislation on tariffs and all the other things, we will be subject not to Westminster ... but subject to the EU," Shannon told CNBC's "Squawk Box." "Makes me less British, less of a Unionist," he said. The new withdrawal agreement that Johnson struck with the EU last week was met with fierce opposition by U.K lawmakers — in particular the DUP, as well as the main opposition Labour Party.

'Worse' Brexit deal than before

On Saturday, U.K lawmakers delayed a vote on the new deal again, leading to Britain requesting the EU to delay the Brexit deadline for the third time. The current deadline for the U.K. to leave the European bloc is Oct. 31. Echoing other opposition lawmakers, U.K. Shadow Justice Minister Yasmin Qureshi told CNBC Sunday night local time that the new agreement was "worse than" the previous one, and doesn't benefit the country. "We believe that we would accept Brexit but with a better deal, not the one that the prime minister has got," said the Labour member of parliament for Bolton South East. "I mean, this is the same prime minister who said it would be beyond imagination that any British prime minister would agree to a border in the middle of the Irish sea. That's exactly what it would create." "The agreement ... doesn't benefit the country, it doesn't benefit the people of this country," Qureshi added. The UK government is keen to have the vote again on Monday, or try to pass the full withdrawal agreement bill through both chambers of the U.K. parliament by early this week.

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