Theresa May has attacked one of her predecessors - accusing Tony Blair of "undermining" the Brexit talks by calling for another referendum.
She called his comments an "insult to the office he once held" and said MPs could not "abdicate responsibility" to deliver Brexit by holding a new poll.
In London last week, Mr Blair said MPs might back a new vote if "none of the other options work".
In response to Mrs May, he insisted that a new referendum was democratic.
"Far from being anti-democratic it would be the opposite, as indeed many senior figures in her party from past and present have been saying," he said.
On Thursday about 10 Labour MPs met David Lidington - who is Mrs May's de facto second-in-command - to argue for another public vote.
Sources close to Mr Lidington said it was "pretty standard stuff" and he was not "planning for or advocating a second referendum".
Many senior Labour figures are deeply uneasy about endorsing another referendum.
The government is also opposed to any further referendum, saying the public made a clear choice when they voted in 2016 to leave by a margin of 51.9% to 48.1%.
BBC political correspondent Chris Mason said Mrs May's criticism of the former Labour prime minister was striking for its anger.
Mrs May said: "For Tony Blair to go to Brussels and seek to undermine our negotiations by advocating for a second referendum is an insult to the office he once held and the people he once served.
She added: "We cannot, as he would, abdicate responsibility for this decision.
"Parliament has a democratic duty to deliver what the British people voted for."
Meanwhile, the PM's chief of staff, Gavin Barwell, has responded to reports in the Mail on Sunday that he told colleagues another referendum was "the only way out of this", saying on Twitter: "Happy to confirm I am not planning a 2nd referendum with political opponents (or anyone else, to anticipate the next question)."
International Trade Secretary Liam Fox, who campaigned to leave the EU, said that if another referendum was held "people like me will be immediately demanding, it's best of three. Where does that end up?"
MPs were due to vote on Mrs May's Brexit deal last Tuesday, but it was postponed when the prime minister admitted it would have been "rejected by a significant margin".
After postponing the vote in Parliament, Mrs May travelled to Brussels to make a special plea to European Union leaders, in a bid to make her deal more acceptable to MPs.
However, the EU said there could be clarification but not renegotiation.
The Labour leadership has been under pressure to call a vote of no confidence in the government.
But Labour frontbencher Andrew Gwynne told the BBC's Andrew Marr: "We can't move to the next stage until Parliament has decided whether or not to back the prime minister's deal."
He said the party would be using "parliamentary tactics" to try to bring the MPs' "meaningful vote" on the deal - which was delayed by the government last week in expectation of a heavy defeat - forward to this week.
Asked whether his party would campaign for Brexit under a Labour deal if there were to be another referendum on the issue, he said: "Let's wait and see. These things are moving very quickly.
"We are a democratic party and we will put our decision to the party members in a democratic way before we decide what the next steps are."
Many of Mrs May's Conservative MPs are concerned that the "backstop" - which is aimed at preventing a hard border in Northern Ireland - would keep the UK tied to EU rules and limit its ability to strike trade deals.
Education Secretary Damian Hinds has told the BBC a second referendum would not end the deadlock over Brexit but might simply extend the impasse.
Speaking on BBC Breakfast, he urged politicians to back the PM's plan, describing it as "balanced" and the "best of both worlds".
Mr Hinds accused some in Parliament of "wishful thinking" in believing they will get something closer to their own view by rejecting Mrs May's deal, adding: "There is really no reason to believe that's true."
Meanwhile, in an interview with the Sunday Telegraph, Foreign Secretary Jeremy Hunt has said the UK will "flourish and prosper" even if it leaves the EU with no deal.
"We've faced much bigger challenges in our history," he said.
"But we shouldn't pretend that there wouldn't be disruption, there wouldn't be risk, and there wouldn't be impact and that's why as a responsible government we have to make all the preparations necessary
He also said he wanted a "crack" at succeeding Mrs May after the PM takes the country through "this challenging next few months".
His comments come after Mrs May made it clear she would step down before the next general election - due in 2022.