LONDON - Conservative frontbencher Gareth Johnson resigned on Monday on the eve of a crucial parliament vote over the Brexit deal scheduled for Tuesday.

Johnson, a government whip, said in his letter to the Prime Minister that he cannot "in all conscience, support the government's position when it is clear this deal would be detrimental to our nation's interests".

The resignation came as Prime Minister Theresa May was battling for a last-minute support for the Brexit deal.

Speaking at a factory in Stoke-on-Trent, May warned that if MPs voted down her deal, the most likely result would be a paralysis in parliament and a risk for no Brexit, which would mean a failure to deliver the result of the 2016 EU referendum.

Johnson said he had spent the last few weeks trying to reconcile his duties to assist the government to implement the withdraw agreement despite his personal objections to it.

"The 'backstop', contained in the agreement, gives our country no clear, unilateral path out of the European Union and ensures we will be fettered in our ability to negotiate trade deals with other nations in the future," he said.

Johnson said the Brexit deal prevented Britain taking back control and instead could leave the country perpetually constrained by the EU, believing it would be "disrespectful" to the referendum result if this agreement were to be implemented.

The controversial "backstop" plan refers to the Irish border backstop, one of the biggest stumbling blocks to the Brexit deal.

"Backstop" is designed to avoid border checks between Northern Ireland and the Republic of Ireland. It is considered by some British especially Brexiteers to be a trap to retain Britain in a customs union with the EU and pragmatically delay their "divorce".

On Monday, European Union leaders wrote a letter to May with assurances, saying that if the Irish backstop were nevertheless to be triggered, it would only apply "temporarily" and in place for as long as strictly necessary.

The EU is determined to replace the backstop solution on Northern Ireland with a subsequent agreement that would ensure the absence of a hard border on the island of Ireland on a permanent footing, according to the letter.

The border that separates Northern Ireland, part of the United Kingdom, and the Republic of Ireland, an EU member state, is among the most difficult issues in Britain's exit from the EU.

The UK and Ireland are currently part of the single market and customs union, so products need not be inspected for customs and standards and have been transported freely.

That could change after Brexit, as Northern Ireland and Ireland would then fall into different customs and regulatory jurisdictions, meaning that products would theoretically have to be checked.

Both London and Brussels committed to avoiding the return of a "hard border" after the UK leaves the EU in March 2019.