Theresa May has said Britain's offer for its divorce bill with the EU will be off the table if the UK does not agree a future partnership with Brussels.
The Prime Minister told MPs the offer, which she said was likely to be between £35 billion and £39 billion, had been made "in the context of us agreeing the partnership for the future".
Labour leader Jeremy Corbyn said the Government had scraped through the first phase of talks, as he challenged Mrs May to drop plans to write the date of Brexit into the European Union (Withdrawal) Bill.
Giving a statement to MPs about progress in the negotiations, the Prime Minister said: "He asked about whether this was conditional on securing a deal.
"It is clear in the joint progress report, I have repeated it in my statement just now, that this offer is on the table in the context of us agreeing the partnership for the future, agreeing the next stage and agreeing the partnership for the future.
"If we don't agree that partnership, then this offer is off the table."
Speaking about the financial settlement, Mrs May continued: "We have agreed the scope of the commitments and methods for valuation and adjustments to those values.
"It is the case that that is, the calculations currently say that that would be £35 billion to £39 billion."
Mr Corbyn said the Prime Minister "has scraped through phase one of the negotiations".
He added: "Scraped through after 18 months, two months later than planned, with many of the key aspects of phase one still not clear.
"This weekend Cabinet members have managed to contradict each other. Indeed some have managed to go even further and contradict themselves."
He went on to challenge Mrs May over a Government amendment to the European Union (Withdrawal) Bill that would write into law Britain's exit date of March 29 2019.
A number of senior Tories have also spoken out against the proposals.
"Has this experience given the Prime Minister reason to consider dropping the unnecessary exit date deadline of 29 March, 2019 from the EU Withdrawal Bill?" Mr Corbyn said.
"Because I'm sure the whole House, and indeed I think probably the whole country, would rather get the best possible deal a little bit later, if that meant a better deal for people's jobs and the economy."
Mrs May, responding to Mr Corbyn's comments, said: "We're leaving the European Union on that date.
"That is what the British people voted for, and that is what this Government is going to put in place."
The Prime Minister earlier said nothing was agreed until everything was agreed, but that there was a new sense of optimism in the talks.
She added: "This is good news for the people who voted Leave, who were worried that we were so bogged down in the negotiations, torturous negotiations, it was never going to happen.
"It's good news for people who voted Remain, who were worried we were going to crash out without a deal.
"We are going to leave, but we're going to do so in a smooth and orderly way, securing a new, deep and special partnership with our friends, while taking back control of our borders, money and laws once again."
Nigel Dodds, the DUP's Westminster leader, thanked Mrs May for her "personal devotion" to working to get the text "strengthened in relation to the constitutional and economic integrity of the whole United Kingdom", and said: "The Prime Minister said at her Friday press conference that the deal arrived at represented a significant improvement from Monday and we in these benches agree wholeheartedly with that."
He asked: "Would she confirm that the text of this agreement now makes clear that in the event of a deal ... Northern Ireland will not be separated politically, economically or by any regulatory requirements from the rest of the UK, along with the aim of no harder border on the island of Ireland, but in the event of no deal - no overall deal - nothing is agreed?"
Mrs May replied: "I'm grateful for the contributions that were made, as I said in my statement, by the DUP and others who were concerned about the union of the United Kingdom - and the joint progress report was strengthened to make absolutely clear, as he says, that of course, under the Belfast Agreement we recognise the principle of consent but we are very clear that nothing in that agreement is going to lead to a separation of Northern Ireland from the rest of the United Kingdom."