MPs are set to vote on blocking a no-deal Brexit on Wednesday in a free vote for the Conservatives on whether they want the UK to leave the EU without a deal at the end of the month.
They will vote on a motion stating "this House declines to approve leaving the European Union without a Withdrawal Agreement and a framework on the future relationship on March 29".
If MPs reject no-deal, as most Westminster observers expect, a third vote will follow on Thursday on whether to authorise Mrs May to request an extension of the two-year Article 50 negotiation process.
Politicians are divided on the plans, with some ardent Leavers arguing that a no deal Brexit is not something to be scared of.
So what is a no deal Brexit and how could it affect the UK?
What is a no deal Brexit?
A no deal Brexit means the UK would leave the EU without having secured a formal withdrawal agreement. The UK is set to leave the EU on March 29, 2019.
What happens now May's deal has failed to win support in Westminster?
Although the 149 margin was reduced from the record 230-vote defeat of the first "meaningful vote" in January, Mrs May was left far adrift from a majority with just 17 days to go to the scheduled date of Brexit.
On Wednesday, MPs will vote on whether to block a no-deal Brexit.
If they reject crashing out without a deal, another vote will take place on Thursday extending Article 50 for further negotiations to take place.
However, the EU has repeatedly said it will not reopen talks on the Withdrawal Agreement.
Some MPs, such as Dominic Grieve and Chuka Umunna, are setting a People’s Vote as their priority and want a second referendum on the terms of a Brexit deal.
A second referendum could also give the public the chance to decide whether it still wanted to go ahead with withdrawal.
What will happen in the event of a no deal Brexit?
Dr Simon Usherwood, a reader in politics at the University of Surrey, told the i that when the UK leaves the EU, "everything associated with that would come to an end".
"[A no deal] doesn’t stop the UK leaving but it means there is absolutely no clarity about what happens," he added.
A no-deal Brexit would allow Britain to try and broker trade deals with other countries, but they take years to complete.
But it would mean the country would not be legally obliged to pay the £39 billion divorce bill.
Under the current deal, the UK can only implement trade deals with other countries after the transition period.
The transition period would allow Britain to make new trade deals with the EU but in a no deal situation, there would be no adjustment time to allow for changes in laws or negotiations for trading deals.
What affect would a no-deal Brexit have on Britain?
EU nationals living in the UK and UK citizens living in the EU could see their residency rights disappear overnight and become subject to domestic immigration rules.
Britain would be able to set a control on immigration and in return Europe could retaliate.
A no deal Brexit threatens to put pressure on the Good Friday agreement, as the EU would want Ireland to impose customs and other checks on its border with Northern Ireland which neither want to do.
On Wednesday, it was revealed that Britain will slash tariffs on the majority of products imported from outside of the EU in the event of a no-deal Brexit.
Should the UK crash out of the EU without a deal, the number of items eligible for zero-tariff access will rise from 80 per cent to 87.
But some products coming from the remaining 27 EU member states which are currently imported free of tariffs would face levies for the first time.
The moves have been slammed by business leaders, branded a "sledgehammer for our economy" while there are warnings cheaper steel imports could "destroy" UK manufacturing jobs.
The largest tariffs would impact poultry meat, 60 per cent, and beef, 53 per cent.
Customs checks at ports would affect the supply of food and goods and there are fears of long queues at borders and disruption to air travel.
Bank of England governor Mark Carney warned that house prices could plummet by a third over three years and that homeowners could be left with negative equity and spiralling mortgage rates.
UK Driving licences may not work abroad and British passport holders could run into difficulty.
It would affect Britain's trade, immigration and customs rules which are aligned with the EU.
Under a no-deal scenario, the UK would be treated as a "third country" by the EU and commerce would be governed by World Trade Organisation rules.