Jeremy Corbyn has called on all Labour MPs to follow him in voting down a flagship Brexit bill, despite government ministers warning defeat would cause chaos and confusion.
Downing Street has said it is confident of victory in the crunch second reading vote on the EU (Withdrawal) Bill, expected early on Tuesday after a debate stretching up to midnight.
But ministers were taking no chances, with Boris Johnson and David Davis issuing last-minute pleas to back the bill, which repeals the 1972 act which took Britain into the European Economic Community and incorporates relevant EU rules and regulations into the domestic lawbook.
Britain's foreign secretary Mr Johnson said defeat would result in a "disorderly" departure from the bloc in March 2019, while Brexit secretary Mr Davis warned: "A vote against this bill is a vote for a chaotic exit from the European Union.
"The British people did not vote for confusion and neither should Parliament."
Mr Corbyn restated his determination to lead Labour MPs into the No lobby, insisting that the bill represents "a power grab by the government at the expense of our democratically elected Parliament", because it would give ministers authority to amend laws without full scrutiny.
Vowing not to hand over powers on issues such as workers' rights and environmental protection to Mr Davis, the Labour leader told BBC Radio 4's World at One: "We will oppose the bill tonight because we want parliamentary scrutiny, we want democratic accountability of the government in how it reacts to the result of the referendum.
"That's why we are voting the way we are tonight and I would urge all colleagues to do the same."
But Labour's former minister Caroline Flint said she would defy the three-line whip.
The Don Valley MP said a defeat for the bill would cause "huge problems" and told Radio 4's Today programme: "I do believe that in respecting the outcome of the referendum, in respecting what I said to my electors in the general election just a few months ago, it is important that we get on with the job of making sure we can have as smooth an exit from the EU as possible."
Former Labour MP Gisela Stuart, a prominent Leave campaigner and chair of the Change Britain group, said opposition to the bill on Monday night would amount to "a cynical vote to disrupt the Brexit process, which the public will not look kindly upon".
The Liberal Democrats, who will oppose the legislation, have urged the Labour leader to sack any frontbenchers who defy the whip or risk his party's shift towards a "softer" Brexit being exposed as a "sham".
Three votes are expected, on a Labour amendment, the main second reading motion and the programme motion, which sets out the time available for MPs to go through the Bill line by line in the Commons.
There are currently a guaranteed 64 hours over eight days for the committee stage, when amendments can be made, but concerns have been expressed by Tory and Labour MPs that this will not be enough time given the constitutional significance of the legislation.
If the government motion setting out the time for debate is defeated, ministers will have to consider an alternative timetable.
Mr Johnson said "we need to get this great ship launched", with the transfer of EU laws onto the domestic statute book a key priority.
"If we don't do that then of course the whole thing will be disorderly and chaotic," he told BBC Radio 4's Today programme.
"People who vote against it will be effectively voting to frustrate Brexit by producing a completely chaotic result."
Signalling that victory on the Brexit bill would mark a key moment for Theresa May's administration, Mr Johnson – widely viewed as a potential candidate in any leadership contest – said: "I am full of confidence and I think that if we can get the vote through tonight – and I very much hope that we will – the programme will go on."
Several Tory MPs have expressed disquiet over the bill but are expected to back it at second reading, the first stage of its progress through the Commons.
But they have warned they are ready to back amendments later in the process, raising the prospect of the minority government being bounced into concessions to avoid defeat in House of Commons votes.
