British Prime Minister Theresa May suffered an early defeat to her Brexit plans on Wednesday when members of parliament demanded the government come up with a plan B.
The parliament demanded the alternative plan should be submitted within days if she loses a vote on her deal to leave the EU.
It is less than three months before Britain is due to leave the EU.
The parliament began a five-day battle over May’s Brexit plan with a show of force – undermining her preferred timetable if MPs vote down her deal on Tuesday.
May has refused to retreat from her unpopular deal, which envisages close trading ties with the EU after leaving in March.
She also prefer to press ahead with the vote that she looks set to lose after failing to win over her nominal Northern Irish allies.
Losing the vote would deepen the uncertainty over the future of Brexit, Britain’s biggest shift in foreign and trade policy for more than 40 years.
The possible loss could open the way for several different outcomes, ranging from a disorderly exit to another referendum.
MPs voted 308-297 in favour of demanding the government come up with an alternative plan within three working days after Tuesday’s vote, rather than a planned 21-day limit.
It was a largely symbolic vote aimed at putting pressure on the government.
There were turbulent scenes in parliament when some in May’s Conservative Party accused the speaker of bias.
May’s spokesman said the government’s advice was that parliament could not change its so-called business motion.
The motion sets out the procedure for the Brexit vote, but played down the impact of the vote for its overall plans.
“We are doing everything we can to win the meaningful vote that happens on Tuesday,” the spokesman said.
“But it is also the intention, if that were not to take place that we respond quickly to provide certainty on the way forward following that vote.”
Combined with a vote late on Tuesday when the government lost on the finance bill, the defeats underline May’s precarious position in parliament and the difficult she will have in winning approval for her Brexit deal.
The opposition Labour Party has said that it will immediately table a vote of no confidence in the government if May loses the vote.
With the likelihood of a no-deal Brexit rising, the EU is looking at how Brexit might be postponed.
Pro-EU campaigners are testing ways Britain could hold another referendum after voters narrowly backed leaving in 2016.
Britain is due to leave the EU on March 29, at 2300 GMT.
The government needs 318 votes to get a deal through the 650-seat House of Commons, as seven members of Irish nationalist party Sinn Fein do not sit, four speakers and deputy speakers do not vote and the four tellers are not counted.