Ed Miliband insisted today the Labour Party was embarking on "real, deep, genuine change" to reconnect with disenchanted voters.
The party's humiliating defeat in the Bradford West by-election was a reminder of the "scale of the task" facing Labour after it was rejected in the 2010 general election, he said.
"You might think the Government's failure to bring about change will be good for Labour," he said in a speech in Derby.
"It certainly didn't turn out that way in Bradford West two weeks ago. The uncomfortable truth for Labour is that people turned to a protest party rather than to us."
The Labour leader said: "People turning away from an unpopular Government doesn't automatically mean they turn to Labour."
Mr Miliband insisted David Cameron's changes to the Conservative Party were only "skin deep" and a lesson to Labour as it seeks to win back power.
"To be trusted to deliver change, we will not make the same mistake as David Cameron," he said.
"Our party is recognising the real changes we need to make. Not hugging a husky then betraying the environment. Or hugging a hoodie and then cutting youth services.
"Real, deep, genuine change, infusing our party, our ideas and our organisation."
Mr Miliband said it was "not good enough" for Labour to point to the Government's "failure" but had to show that the party is "rooted in communities".
"The next election will be about us as much as them," he said.
"It is a changed Labour Party that is standing in these local elections and we will continue to change."
Speaking during a question and answer session at the Joseph Wright Centre in Derby, with an audience of around 100 people made up of members of the public and Labour supporters, Mr Miliband said the issue and problems surrounding "fourth party politics" had to be confronted to restore faith in the party.
He said: "In Bradford only four out of 10 voters supported the three mainstream political parties.
"The fourth party who says 'a plague on all your houses' is an issue we've got to confront.
"Now how do we confront it?
"By showing what we all believe, which is that we can make a difference to people's lives.
"George Galloway is not going to make a difference to the lives of people in Bradford.
"He's made a whole series of promises he knows he can't keep.
"Someone even told me he'd made promises to people in Bradford that he was going to cut their taxes.
"He's got no power to cut their taxes.
"The best answer to it is, first, a Labour Party that shows it can make a difference and secondly, and this is important, a Labour Party that is on the doorsteps."
Speaking after the hour-long event, Mr Miliband also said the party must pay attention to the lessons of the last general election.
He said: "I think what's really important is that we recognise that we were rejected two years ago at the general election of 2010 and we are a changed party in that we are showing that we can deliver even in tough times, even when there's less money around."