Sir Keir championed Labour s push for a referendum on the final Brexit deal and insisted that Remain would be an option on the ballot paper as Corbyn s Brexit Secretary.
She is aiming to win support from MPs ahead of a crucial vote on December 11.
Here are the key points you need to know from day one of the debates.
MPs gathered in the House of Commons for the first of five days of debates (PA)
Day of defeats
Before the debate could even get going, Mrs May suffered a series of bruising Commons defeats which saw her authority take a pounding.
Ministers had to agree to publish the “final and full” legal advice on the withdrawal agreement as the Government was found to be in contempt of Parliament for not already doing so.