'We may not agree on everything, but through debate and discussion... ideas can be clarified and improved and a better way forward found. "We can play it safe or we can strike out with renewed courage and vigor, making the case for our ideas and values and challenging our opponents to contribute, not just criticize".
Together, the new group could spell trouble for the Prime Minister as she tries to steer Brexit legislation through the House of Commons.
Acknowledging that she now faces a "rather different" reality, she will promise to "take big decisions in the long-term interests of Britain". At this critical time in our history, we can either be timid or we can be bold.
"In everything we do, we will act with an unshakeable sense of goal to build the better, fairer Britain which we all want to see".
May's ability to carry on as prime minister and drive divisive Brexit legislation through parliament with only a fragile majority behind her has been persistently questioned since the election.
Diehard Tory Remainers are plotting with Labour to force Mrs May to back down over her insistence that European judges should be barred from meddling in the United Kingdom after Brexit.
Last night, however, the prime minister was looking isolated within her own party amid growing talk of replacing her before its autumn conference.
It comes as former Brexit minister David Jones whined in a Mail on Sunday column that "fanatically pro-EU MPs" were joining forces to keep the United Kingdom in the single market and customs union.
Ms May will return to her core message from when she succeeded David Cameron: a "commitment to greater fairness" and tackling "injustice and vested interests" in recognition that the European Union referendum result was a "profound call for change across our country".
She will launch a review - of casual and low-paid work - by Matthew Taylor, a former top adviser to Tony Blair, which she commissioned when she became prime minister.
In her speech, the PM will say that though the result of June's election was not what she wanted, "those defining beliefs remain, my commitment to change in Britain is undimmed".
"I am convinced that the path that I set out in that first speech outside Number 10 and upon which we have set ourselves as a Government remains the right one".
But she will also acknowledge her weakened position in Parliament, with an appeal to Labour to help deliver "bold" reforms.
Shadow communities secretary Andrew Gwynne said: "Theresa May has finally come clean and accepted the Government has completely run out of ideas".
May's weakened position, having lost her majority and now trailing the opposition Labour Party in opinion polls, has reopened the debate over how Brexit should unfold, with some of her own most senior ministers now emboldened to disagree with her. There were also reports that a "kamikaze" group of right-wing Tory MPs are ready to risk handing power to Labour because "a brief dose of a Corbyn Government" would end in disaster and provide a long-term boost to the Tories.
"This is further evidence that this Government can no longer run the country".
"We won't accept MPs being treated as spectators in the Brexit process, when we should be on the pitch as active players representing our constituents", said Umunna, who led the Labour rebellion against leaving the single market last month.
"A call for Labour to contribute is superfluous".
May, who took office on July 13, 2016, insists she will still be prime minister in 2018, despite losing her majority.