The British government will offer parliament a take-it-or-leave vote on any final EU departure agreement, Brexit secretary David Davis said on Monday.
Mr Davis's move was seen as an attempted concession to Conservative rebels who may defy the government this week by voting against Brexit legislation transferring EU laws to Britain.
However, the bid to head off opposition from lawmakers was met with criticism as MPs claimed the vote would be meaningless and give them little time to consider any eventual Brexit deal.
Mr Davis confirmed that if parliament votes down the withdrawal bill, Britain would leave the European Union with no Brexit deal at all.
And he said there would be no withdrawal agreement bill, or vote, if Westminster cannot strike a deal with Brussels.
"If we don't have a withdrawal agreement we can't have a withdrawal agreement bill. Full stop."
Details of the bill are tied to ongoing and future negotiations, which will not be revealed until the talks are near completion.
"Once we have reached an agreement we will bring forward a specific piece of primary legislation to implement the agreement," Mr Davis told MPs.
_______________
Read more
[ European Union signs landmark new defence pact ]
[ Russian involvement in Brexit vote revealed by Twitter data analysis ]
[ EU Brexit chief preparing for 'possible' failure ]
_______________
Prime minister Theresa May's governing Conservatives rely on support from Northern Irish unionists for a narrow majority in parliament.
But the proposal triggered an immediate backlash from rebels within Mrs May's party.
Conservative MP Heidi Allen said the move was "pointless" and offered "no safeguard if no deal is reached".
Fellow backbencher Antoinette Sandbach said it was "meaningless" if the timetable slipped beyond the March 2019 EU exit date.
Labour MP Chuka Umunna, co-chairman of the cross-party parliamentary group on EU relations, said the move was "totally insufficient" and gave "no guarantee of a meaningful vote".
He said the bill must be amended "to provide for a proper, not a fake, meaningful vote before any exit day".
Chris Leslie, also from the main Labour opposition, called it a "sham offer" that was "totally worthless".
"This is a post hoc, after-the-horse-has-bolted piece of legislation," he said.
"Parliament could do nothing at all to shape the nature of that withdrawal agreement."
The Brexit ministry said the bill was expected to cover issues such as the rights of EU citizens in Britain and British nationals in the EU, separation payments and an agreement on any post-Brexit transition period.
Keir Starmer, Labour's Brexit spokesman, said the proposed law was "a significant climbdown from a weak government on the verge of defeat" in a series of upcoming lawmaker Brexit debates.
"For months, Labour has been calling on ministers to guarantee parliament a final say on the withdrawal agreement... They have finally backed down," he said.
