Prominent Brexit supporter and leader of the House of Commons Andrea Leadsom announced her resignation from British Prime Minister Theresa May's cabinet on Wednesday evening.
The move came as pressure mounted on May to quit after MPs tore into her new Brexit plan.
Another Conservative MP, writing an opinion piece in the Financial Times, called for her to step down.
"There is one last chance to get it right and leave in an orderly fashion. But it is now time for Prime Minister Theresa May to go and without delay," said Tom Tugendhat, who added that her attempt to deliver Brexit.
Earlier opposition leader Jeremy Corbyn said May had lost control of her Conservative Party and called for a general election to break the Brexit stalemate.