"Profound" changes to the Labour Party on the scale of Tony Blair's New Labour reforms of the mid-1990s have been promised by leader Ed Miliband.
In a newspaper interview, published as he returns from two weeks' paternity leave, he warns his party that it faces a "long, hard road" ahead.
The party will review its policies and its organisation, including the rules for electing its leaders, he says.
A commission on Labour's organisation will be launched at the weekend.
The aim is to turn the party into the "largest community organisation in the country", Mr Miliband tells the Guardian.
The Labour leader - elected in September - also addressed MPs at a meeting in the House of Commons.
He said it was frustrating to watch the "terrible" things the Conservatives and Liberal Democrats were doing in power.
Mr Miliband added that Liam Byrne, the shadow Cabinet Office minister, would be carrying out the policy review, and was starting with a "blank page".
In his newspaper interview, he dismissed claims he had been too low-profile since winning the Labour leadership, saying: "It's about digging in, and it's not about short-term fixes, nor shortcuts to success."
"There is a long, hard road for us to travel," he told the Guardian. "I am talking about change as profound as the change New Labour brought, because the world itself has changed massively, and we did not really change fundamentally as a party, or come to terms with the changes, and have not done so since 1994."
The commission will cover the issue of leadership elections, including the influence of the unions.
During the Labour leadership campaign, in which MPs, party members and trade unionists were balloted, Mr Miliband secured the backing of the leaders of three of Britain's four biggest trade unions.
His older brother and leadership rival, David Miliband, won a majority of support from Labour MPs at Westminster and party members, but Ed was ahead among members of trade unions and affiliated organisations.
Ed Miliband appeared to reject the idea that union members should lose their role in choosing the Labour leader, saying those paying levies to the party had a "link to working people in the country and we've got to be linked to them".
In an indication of the tax policy he intends to pursue, he suggested that he would support the retention of the 50p top rate of income tax into the future.
'Beyond New Labour'
Shadow chancellor Alan Johnson has said previously that Labour "might not see the need for a 50p tax rate in five years' time".
But Mr Miliband said the tax rate was not simply about cutting the deficit: "It's about values and fairness and about the kind of society you believe in and it's important to me."
Britain remained a "fundamentally unequal society", he said, adding that the plan was to "move beyond New Labour".
"Here's the paradox of Britain today," he said. "Is Britain materially better off than it was 20 to 30 years ago? Yes, absolutely it is. But for some people the gap between the dreams that seem to be on offer and their ability to realise them is wider than it's ever been before, and it seems much more of a struggle and that's what interests me.
"How do you close that gap between the dreams that are apparently on offer and people's ability to realise them? And I think the [coalition] are widening that gap."
Asked whether Mr Miliband had failed to make an impact since winning the leadership, shadow business secretary John Denham said it was not the time to give "a series of headline-grabbing, detailed pledges, which would undoubtedly look out of date in four years' time".
He told BBC Radio 4's World at One: "We need to take the time to talk to voters."
A Conservative spokesman said: "Ed Miliband can't promise us another plan when he hasn't fulfilled his last promise to give us his own credible deficit reduction plan.
"If he really wants to review his party policies, he should start by asking his shadow chancellor why he opposes him on the 50p rate and a graduate tax."