David Cameron told Conservative MPs tonight he would 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 last 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 last night 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 last 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."
On Tuesday night a "very angry" David Cameron was said to have confronted a leading Tory Lords reform rebel, in bust-up that ended with the MP leaving the parliamentary estate.