David Cameron has told Conservative MPs that he will only make one more attempt at winning their support for House of Lords reform before he would "draw a line" and move on.
At a meeting of his parliamentary party in the Commons following Tuesday night's rebellion, the Prime Minister also raised the prospect of watering down the plans with a "smaller elected element" for the second chamber.
His comments risked inflaming tensions with his Liberal Democrat coalition partners - who are deeply wedded to the reform - and may embolden Tory backbench rebels scenting victory within a few months.
Mr Cameron's efforts are concentrated on securing enough support by the end of the summer to pass a timetable motion for the House of Lords Reform Bill - ensuring it does not bog down the rest of the parliament as opponents try to talk it out. The Government averted a major defeat on such a motion by withdrawing it at the eleventh hour.
Speaking to the 1922 Committee, Mr Cameron said there would be no deal with Labour - who had threatened to vote against Tuesday night's motion despite backing the Bill's Second Reading - because they "cannot be trusted".
"There is not going to be endless haggling with the Lib Dems either. We are going to have one more try to see if we can secure a way forward and achieve a smaller elected element," the Prime Minister said. "If we fail to do that then we need to draw a line. We are not going to go on and on with this and damage the rest of the Government's programme."
Mr Cameron, whose authority was damaged by a 91-strong rebellion by Tory MPs against Lords reform on Tuesday night, was warned by Lib Dem Deputy Prime Minister Nick Clegg earlier that they had entered a "contract" to get the plans through.
"A deal's a deal and it's important you stick to that deal and you stick to the contract, if you like, that you have entered into," Mr Clegg said. "That's why I think it is important - not least because so far both parties have stuck to that deal very effectively - that we continue to do so. That's why it is important that we deliver House of Lords reform, because it's a clear commitment in the Coalition Agreement."
The programme motion was abandoned on Tuesday with the agreement of Mr Clegg on the understanding that the Prime Minister needed more time to win over his MPs to the issue. Sources close to the Deputy Prime Minister insisted on Tuesday night that there was no plan to change the legislation.
A senior Liberal Democrat source said: "We're pleased that the Prime Minister has confirmed to the 1922 Committee that he is committed to trying to get Lords reform through the House. The Coalition Agreement commits the Government to a wholly or mainly elected Lords."