On Tuesday, the government averted defeat in passing the Customs Bill by only 6 votes (307 to 301), after 12 pro-European Union (EU) Tory MPs rebelled to back an amendment.
The prime minister survived a backbenchers' rebellion demanding a customs union deal with the EU - but lost a separate vote demanding free flow of medicines across Europe post-Brexit.
The Government's Customs Bill, which paves the way for a trade deal with the European Union, was approved by 318 votes to 285 on Tuesday night.
She also saw off an attempt by pro-European Union rebels in her own party require the government to try to negotiate a customs union arrangement with the EU if, by January 21, 2019, it had failed to negotiate a frictionless free trade deal with the bloc.
This article has been adapted from its original source.
A series of key votes were held in the House of Commons on Monday, including one which put on a legal footing the UK's position that Northern Ireland can not have a customs arrangement separate from the rest of the UK.
On Tuesday evening the Prime Minister fought off the threat of the United Kingdom being locked into a customs union after Brexit.
Remain MPs were left furious last night after four amendments to a tax bill, tabled by hard-line Brexit lobby group European Research Group, were backed by Mrs May.
The taoiseach also said his government needed to "step up our preparations for a no-deal scenario" but added that such an outcome was unlikely.More news: Groenewegen wins longest Tour stage
Frank Field, Kate Hoey, John Mann and Graham Stringer - (plus now suspended Kelvin Hopkins) joined the majority of Tories in the voting lobby to defeat the customs union amendment, "New Clause 18".
She must now try to ensure that the United Kingdom continues to participate in the regulatory network operated by the European Medicines Agency.
The government said being part of an EU customs union would prevent it from striking global trade deals, won the vote by 307 to 301, a slim majority for May of just 6.
"Problem is, I don't think that she's in charge anymore".
The prospect of continued drama in parliament and doubts over the future of May's "white paper" Brexit plan - which is itself only a starting point for talks with the European Union - is testing the patience of businesses that depend on cross-border trade.
The MP for Broxtowe told BBC Radio 4's Today programme she would be the first in the queue to give a vote of full confidence in the prime minister. The vote saw three Labour MPs and a former Labour MP-who now votes as an Independent-vote with the government.
The motion passed by Vauxhall Momentum reads: "As Labour members who campaigned for Kate Hoey at the last General Election despite many of us disagreeing with her about Brexit, we are appalled at the way in which she is demonstrating that her personal views take priority over representing her constituents and our Party by voting to enable this rotten, inept Government to stay in office".