British Prime Minister Theresa May begins a major parliamentary battle over Brexit on Tuesday, facing competing demands by MPs to change her strategy as tensions rise among her scandal-hit ministers.
MPs will have their first chance to scrutinise the EU Withdrawal Bill, which would formally end Britain's membership of the European Union and transfer four decades of EU legislation into UK law.
The government faces potential defeat on key amendments to the bill if rebel Conservative MPs ally with the main opposition Labour Party, increasing the risks for May's perilously weak minority government.
The government said it would ensure legal certainty when Britain leaves the bloc in March 2019.
But critics warn the EU Withdrawal Bill -- also known as the Repeal Bill -- represents a power-grab by ministers, while others see the legislation as a chance to shape May's Brexit policy.
Lawmakers -- including members of May's own Conservative party -- have tabled 188 pages of amendments to the bill, which will be debated in groups over eight days spread over the coming weeks.
The showdown comes as the prime minister, weakened by a June election in which she lost her parliamentary majority, struggles to assert her authority even over her own cabinet.
Two ministers have quit in the past fortnight -- one over sleaze, the other accused of effectively running her own foreign policy -- while two others stand accused of instructing May how to run Brexit.
The premier is also under increasing pressure from Brussels to come up with a financial offer to keep negotiations on track, with a crunch summit of EU leaders looming in mid-December.
Sterling dropped on Monday amid reports that dozens of Conservative MPs were backing a move to oust May.
In the first skirmish on the Repeal Bill on Tuesday, the opposition Labour party will seek a vote on an amendment that would extend Britain's membership of the EU's single market and customs union, and the jurisdiction of the European Court of Justice, into a transition period.
The government said it wants an implementation period of around two years after Brexit to stop an economically damaging "cliff-edge" -- but insists Britain will be fully out of the EU.
To that effect, it has tabled its own amendment putting the date of Britain's departure onto the face of the bill, which is likely to be debated later on Tuesday, although not taken to a vote.
But this has angered some Conservative MPs.
One of them, former attorney general Dominic Grieve, told AFP it was "utterly pointless and counterproductive" and would remove any flexibility in case the negotiations were delayed.
The toughest votes are expected in the coming weeks, as Grieve and other Conservative MPs seek to reduce the powers the bill gives to ministers to change EU laws as they are transferred across.
On the eve of the debate, the government made an apparent concession to rebels by promising a separate piece of legislation that would allow parliament to have a binding vote on any Brexit agreement.
Keir Starmer, Labour's chief Brexit spokesman, said the proposal was "a significant climbdown from a weak government on the verge of defeat".
However, Brexit Secretary David Davis conceded that even if MPs failed to back that legislation -- the Withdrawal Agreement and Implementation Bill, Britain would still leave the EU on March 29, 2019.