UK Conservative whip Gareth Johnson, who helped enforce discipline in Prime Minister Theresa May's Conservative Party, quit his role on Monday over her Brexit deal with the European Union which faces a crucial vote in parliament on Tuesday.

"Over the last few weeks, I have tried to reconcile my duties as a Whip to assist the Government to implement the European Withdrawal Agreement, with my own personal objection to the agreement," Gareth Johnson wrote in a resignation letter to May which he also posted on his Facebook page.

"I have concluded that I cannot, in all conscience, support the Government's position when it is clear this deal would be detrimental to our nation's interests."

"I believe it would be disrespectful to the referendum result if this agreement were to be implemented," 

His resignation comes one day before UK parliament's delayed vote on British Prime Minister Theresa May's Brexit deal.

(With inputs from Reuters.)