The main opposition Labour Party is planning to table several changes to the repeal bill created to keep Britain in the single market and customs union during a Brexit transition period after 2019, according to The Times.
A handful of Labour rebels could vote with the government, but the Scottish National party and Liberal Democrats also plan to vote against the bill after tabling amendments setting out their reasons for opposing it.
Sir Keir - who insisted the policy did not amount to a U-turn but was a mere "development" - stressed the transition period should be "as short as possible", possibly two years.
The Government insists Henry VIII powers contained in the Bill will not be used to make significant changes, and only to make technical amendments to European Union law through secondary legislation. He did say Britain was likely to end up paying money into the European Union budget after Brexit for access to cross-border schemes like space and nuclear research, though the sum would not be large over the medium to long-term.
"The Repeal Bill delivers the result of the referendum by ending the direct role of the European Union in United Kingdom law, but it is also the single most important step we can take to prevent a cliff-edge for people and businesses, because it transfers laws and provides legal continuity", she said.
Influential cabinet figure and key Theresa May loyalist Damian Green has warned Conservative MPs to "back Brexit or get Jeremy Corbyn". "No Conservative wants a bad Brexit deal, or to do anything that increases the threat of a Corbyn government".
Paul Goodman, editor of ConservativeHome and former Tory MP said: "As matters stand, our judgement is that as matters stand she doesn't have enough backing within either Party members or Conservative MPs to see her words of last week through".
"No 10 has been briefing nonsense, and in the knowledge there would be no rebellion".
He told the Commons: "Last week we turned our considerations to the next round of talks and in that my message to the Commission was, let's continue to work together constructively but put people above process". "This attempt to replicate House of Cards tactics is pathetic and is backfiring".
Some of the criticism, including from Tories, has focused on the so-called "Henry VIII" powers to change laws without full parliamentary scrutiny.
"This reckless threat to vote against the Bill, without presenting any alternative approach, risks defying the result of the referendum, and risks the most chaotic ofBrexit scenarios, where our legal systems and institutions can not function from day one of our exit".