Theresa May has said powers to delay Brexit will only be used in "exceptional circumstances for the shortest possible time".
The Government is on course to avoid a second bruising Commons defeat after the Prime Minister reiterated its official support for amendments designed to ease Tory fears over fixing the date of EU withdrawal.
Brexit minister Steve Baker has added his name to proposals tabled by senior MPs including Sir Oliver Letwin and Bernard Jenkin, which emerged last week as a compromise following the Government's first defeat over the European Union (Withdrawal) Bill.
The Government initially tabled an amendment to fix the date of Brexit at March 29, 2019, at 11pm, and to remove the power of ministers to appoint exit day by regulations.
But amendments 399 and 400, which first appeared under the names of the backbench Tory MPs, enable the date to be included in legislation while also giving ministers the flexibility to change it if needed.
Senior Tory Julian Lewis asked for assurances that the provisions set out in amendment 400 to "change the date of our leaving the EU will be invoked only if at all under extremely exceptional circumstances and only for a very short period".
Mrs May said she was happy to give that "reassurance", and replied: "We're very clear we will be leaving the EU on March 29 2019 at 11pm.
"The Bill that is going through though does not determine that the UK leaves the EU, that's part of the Article 50 process and it's a matter of international law and it's important, I think, that we have the same position legally as the European Union and that's why we have accepted the amendment from (Sir Oliver).
"But I can assure (Mr Lewis) and the House we would only use this power in exceptional circumstances for the shortest possible time, and an affirmative motion will be brought to the House."
Tory MPs who rebelled and helped defeat the Government over allowing Parliament a meaningful vote on any Brexit deal are among those to have backed amendment 400, signalling a second damaging defeat is not on the cards.
They include former attorney general Dominic Grieve, former education secretary Nicky Morgan and former communities minister Bob Neill.
The Bill is currently on its eighth and final day at committee stage, which will see MPs finish their line-by-line assessment of the measures which transfer European law into British law.
Mr Grieve began with a criticism of schedule five of the Bill, which requires the Government to publish copies of EU law to be retained in UK law.
Under the same schedule ministers are given the power to make exceptions if they are satisfied that it "has not" or "will not" become UK law on exit day.
Mr Grieve raised concern that there did not appear to be "any limitations" on that power and there "doesn't appear to be any guidance" on when such action might be appropriate.
Earlier in the debate Labour former minister Chris Leslie also called for the publication of retained direct EU legislation.
Mr Leslie, in his new clause 21 to the Bill, asked for publications to be accompanied by "plain English" explanatory notes.