LONDON (NYTIMES, AFP) - Britain's Parliament grabbed control Monday (March 25) of the government's efforts to leave the European Union, challenging the country's political traditions and inflicting on Prime Minister Theresa May a rebuke not suffered by any recent predecessor.

By stepping into the Brexit process and trying to define an alternative path, lawmakers could create a constitutional showdown in Britain, where the government normally controls the agenda in Parliament, especially on its most pressing issues.

Parliament passed an amendment giving itself the power to vote on alternatives to the government's Brexit plan. Its attempt to take control of the process came as May prepared for a last-ditch effort to persuade lawmakers to support her withdrawal plan, which has already been rejected twice by huge margins.

On Monday she admitted that there was "not sufficient support" to make another quick attempt to push it through, though she might try again Thursday.

May's grip on power is ebbing, with members of her Cabinet openly discussing contradictory Brexit policies, rumors swirling of a plot to replace her and several of her Conservative Party lawmakers calling on her to name a date for her departure from power.

She has already said she will not lead the party into the next general election scheduled for 2022.

The latest manoeuvres come at the start of a week that was supposed to see Britain leaving the European Union, something that May had promised more than 100 times would happen on March 29. Instead, Britain will remain at least until April 12, though what happens thereafter is anyone's guess at the moment.

Parliament's attempt to take control was led by Oliver Letwin, a veteran Conservative lawmaker, and is driven largely by fear of leaving without an agreement, a rupture that could leave ports jammed and cause huge economic dislocation.

Richard Harrington, who had warned of the risks of leaving the European Union without an agreement, resigned his post as business minister in May's Cabinet in order to support the amendment.

Under the amendment brought forth by Letwin, which passed by a vote of 329-302, Parliament will hold a series of votes Wednesday on alternatives to May's plan.

MPs will now have the chance to vote on various options, such as revoking Article 50 and cancelling Brexit, holding another referendum, a deal including a customs union and single market membership or leaving the EU without a deal.

But even if MPs decide a majority course of action, the government is not legally bound to follow their instructions.

"The government will continue to call for realism - any options considered must be deliverable in negotiations with the EU," the Brexit ministry said. The prime minister earlier said she was "sceptical" about the process, saying similar efforts in the past "produced contradictory outcomes or no outcomes at all".

'National embarrassment'

May admitted Monday she had still not secured the votes needed to get her own, twice-rejected Brexit deal through parliament, raising again the prospect that Britain could crash out of the European Union in just over two weeks' time.

Anxious at the deepening crisis in London, EU leaders last week agreed to postpone Brexit to avoid a potentially catastrophic "no deal" divorce on March 29, when 46 years of ties were formally scheduled to end.

But they warned that unless May can persuade MPs this week to support her withdrawal deal, Britain must come up with a new plan by April 12 - or leave its closest trading partner with no deal at all.

Opposition Labour leader Jeremy Corbyn said the government was a "national embarrassment", adding: "We will still face the prospect of a disastrous no-deal Brexit."

The EU had earlier ramped up the pressure by announcing its full readiness to deal with the "increasingly likely" event of a no-deal Brexit in three weeks' time.

'Chicken who bottled Brexit'

The British parliament remains deeply divided over Brexit, reflecting the sharp divisions in the country. MPs have already voted against a "no deal" Brexit but this remains the default legal position unless they agree an alternative.

May went over her own Brexit scenarios at an emergency Cabinet meeting earlier Monday. It followed a weekend of media reports that her own ministers were trying to oust her. Most of the alleged plotters are Brexit backers who fear the terms of Britain's departure will be watered down or even reversed.

"Theresa May is the chicken who bottled Brexit," former foreign minister Boris Johnson wrote in a weekly column for The Telegraph.

"It is time for the PM to channel the spirit of Moses in Exodus, and say to Pharaoh in Brussels - LET MY PEOPLE GO," he wrote, leaving some room however for possibly supporting her deal.

What happens to her premiership if parliament favours a more EU-friendly Brexit alternative that contradicts her policies is unclear. Parliament is thought most likely to rally around the idea of keeping Britain in a customs union with the European Union or its single market. Both of those policies contradict May's position.

A customs union would keep Britain from striking its own trade agreements with non-EU countries. A single market would require the government to go back on May's promise to regain control of Britain's borders and migration policy.