LONDON (Reuters) - A lawmaker, 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.

“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.”