Rishi Sunak insisted showing the public “who is really on their side” will set the Tories on the path to victory at the next general election.
The Prime Minister addressed Conservative backbenchers at a meeting of the 1922 Committee on the eve of today’s by-elections.
Mr Sunak braced his MPs that they face a “tough battle” to hang on to Uxbridge and South Ruislip, Selby and Ainsty, and Somerton and Frome.
But he pledged to “throw everything” at winning the next general election.
The PM was understood to have Tory backbenchers: “In the coming months, I am going to set out more of what I would do if I had a full term.
“I was recently described as a full spectrum modern Conservative and you are going to see that in the programme I lay out.”
Mr Sunak pledged to show the public “who is really on their side”, adding: “And that is what will propel us to victory.”
He urged MPs to unite ahead of a general election expected next year.
Mr Sunak said: “When we come back in September we have a choice to make, all of us. Do we come together and throw everything at winning the next election or not? I’ve made my choice, I’m all in with you to win.
“I promise you we can do this but we can only do it together as one team.”
It comes as people are taking to the polls today for the three by-elections in what were seen as safe seats for the Conservatives.
Labour hopes to snatch Uxbridge and South Ruislip, which was Boris Johnson’s seat until he sensationally quit, and Selby and Ainsty – vacated by his ally Nigel Adams’s resignation.
The Lib Dems are eying victory in the contest in Somerton and Frome that was triggered by David Warburton exiting after admitting cocaine use amid allegations of sexual harassment.
Losses for the Tories in all of them would be the first time in 55 years that a government has been defeated in three by-elections on the same day.
