LONDON — Embattled British Prime Minister Theresa May is warning lawmakers they could take Britain into "uncharted waters" and trigger a general election if they reject her Brexit deal in a crucial parliamentary vote this week.

May is fighting to save her unpopular Brexit plan and her job ahead of a showdown in Parliament planned for Tuesday, when lawmakers are widely expected to reject the Brexit divorce deal she struck with the European Union.

Her Downing Street office insisted that the vote will go ahead amid speculation the government may be forced to delay it.

A defeat in the vote could leave Britain crashing out of the EU on March 29, the date for Britain’s exit, with no deal in place — an outcome that could spell economic chaos.

In an interview with the Mail on Sunday, May said rejecting her deal would “mean grave uncertainty for the nation with a very real risk of no Brexit or leaving the European Union with no deal.”

“When I say if this deal does not pass we would truly be in uncharted waters, I hope people understand this is what I genuinely believe and fear could happen,” she said.

She also threatened that not backing her would empower the opposition Labour leader.

“I believe Jeremy Corbyn getting his hands on power is a risk we cannot afford to take,” she added.

Meanwhile former British foreign minister Boris Johnson said on Sunday that May could stay on as prime minister and go back to Brussels to renegotiate the divorce agreement if she loses Tuesday's vote.

Johnson, a leading Brexit campaigner who is seen as a possible successor to May, said Brussels would listen if she asked for the removal from the deal of the Irish "backstop," an insurance policy designed to prevent a post-Brexit hard border between E.U. member Ireland and British-ruled Northern Ireland.

Asked if she could stay on as leader and go back to the E.U. to renegotiate the deal if she loses the vote, Johnson told the BBC: "Of course, that is exactly what needs to happen."

"What people want to hear now is not stuff about leadership elections and personalities, what they want to hear is that there a plan to get out of this mess," he said.

E.U. leaders have insisted the divorce agreement is final and not renegotiable. However, while the 585-page withdrawal deal is set, the declaration on future relations between Britain and the bloc is shorter and vaguer and may be open to amendment.