Shadow international development secretary Mary Creagh has joined the race to succeed Ed Miliband, promising to "earn back the trust that middle England has lost in the Labour party".
Writing for the Daily Mail, Ms Creagh said Labour had forgotten the lessons that saw it to three consecutive general election victories.
The fifth declared candidate for Labour leader, the Wakefield MP joins Liz Kendall, Chuka Umunna, Andy Burnham and Yvette Cooper in the battle to replace Mr Miliband in the wake of last week's election defeat.
Nominations for leader close on June 15th . Members and supporters who sign up by August 12th will be entitled to vote and the result will be announced on September 12th.
In an article revealing her plans, Ms Creagh said: “Tomorrow I am launching my bid to be the leader of the Labour party. I want to earn back the trust that middle England has lost in the Labour party.
“We forgot the hard-learned lessons of our last three election victories; that to win elections a party needs to offer hope.
"Labour didn't just lose middle England last week. We lost Scotland and our industrial heartlands as well."
Ms Creagh said Labour lost because the electorate did not trust the party with the economy.
"Our campaign message focused almost exclusively on the NHS, an emotive issue for many of us, but in the end, not people's main motivation for voting.
“People felt that Labour didn’t understand their aspiration to earn money and provide a better life for their family.
“People trust Labour to look after their schools, hospitals and council services. But they simply do not trust us to run the economy and make them better off. That must change.”
Ms Creagh said later on the BBC: “I think we want to build back a party that understands the hopes and dreams of British families and that can marry aspiration with compassion.
“I think everyone who is standing in the leadership election was part of a shadow cabinet that stood on a platform at the last general election which has been rejected by the British people. I think we need to learn the lessons of that.
“The lessons are that people don’t trust us on the economy, I think people feel they trust us locally in their town halls . . . but when it came to putting the cross next to the Labour candidate at a general election, they decided to go with the Conservatives.”
Earlier, shadow home secretary Ms Cooper, who was treasury chief secretary when the economic crisis struck in 2008, acknowledged the party did not always spend public money “wisely” during its time in office.
Ms Cooper, who declared her candidacy yesterday, said: “The deficit at the time was something like 0.6 per cent (of GDP) — the current deficit. All the political parties at the time were all supporting the spending plans and that was all due to come down.
“There has been a focus on that as if that was the economic issue. The real economic issue of the time was that we had banks who were involved in huge private lending, that nobody had spotted the scale of private sector debt that had been growing up that was unsecured, the links between the financial sector all over the world, particularly into the housing market crisis in America.
“Should the Labour government have done much more to deal with that? Yes, absolutely. Should we have had much stronger regulation of the banks? Yes, absolutely.”
During a visit to a primary school in Sheldon, Birmingham, Ms Cooper dismissed claims that she was too close to Labour’s “old guard” to make the party electable again.
"We've had a lot of people talking about whether or not we can just go back to remedies of the past, be that of Tony Blair or Gordon Brown or other approaches .
“That’s not going to work because the world has changed, the economy has changed.”