Today's Labour politicians could not have created the NHS because they do not have the courage for big ideas, leadership hopeful Andy Burnham will say in a campaign speech.
In an address marking the 70th anniversary of the radical Attlee Labour government, Mr Burnham will say he has become "increasingly disillusioned" by his party's drift away from the voters.
And he will warn a "timid" Labour Party it had become "frightened of its own shadow" as he moves to get back on the front foot as the contest becomes dominated by left-winger Jeremy Corbyn.
In a stark message ahead of ballot papers being sent out next month, Mr Burnham will say: "This week marks the 70th anniversary of the election of the Attlee Government.
"You would think that would be cause for joyous celebration, but I mark it with a sad realisation that the modern Labour Party could not have created the NHS.
"It has become frightened by its own shadow and does not have the courage or capacity to do it."
Mr Burnham will claim the leadership election, triggered by the resignation of Ed Miliband in the wake of May's devastating defeat, had told him Labour members wanted a "different style" of politics and a "break with the bad habits of the past".
Speaking in Leeds, Mr Burnham will say: "It is in this context that we need to judge the current leadership race and ask why Jeremy Corbyn is having such an impact.
"The worst possible response to his impact is to resort to negativity and dire warnings of 'oblivion'. To do that is to mis-read the mood of the moment.
"What our members are telling us is that they are yearning for a different style of politics from Labour and a break with the bad habits of the past. They are sick of politicians speaking in soundbites, sticking to the script and looking like they don't believe a word they are saying.
"At the moment when the challenges we are facing are getting bigger, modern politics has gone in the opposite direction – pettier and smaller."
Mr Burnham is due to outline five challenges Labour must meet - the desire of people to have a decent home, secure job, a good standard of living, good schools and quality care for the elderly.
He will argue: "They are not being given any answers by the identikit politicians appearing on their TV screens. The people haven't drifted away from Labour; Labour has drifted away from them.
"I have lived through this and become increasingly disillusioned.
"We've lost the confidence to think big and provide substantial answers to the modern challenges. We will only win again when we inspire people with our ideas."