Labour former cabinet minister Andy Burnham has confirmed he will stand to be the mayor of Greater Manchester, declaring that Westminster politics had become an "irrelevance" for many people.
The shadow home secretary, whose decision to run was inadvertently revealed in a Twitter blunder, said the Greater Manchester role was a "Cabinet-level job" and Labour had to take the devolution of power seriously.
The former leadership contender's decision to seek a political future outside Westminster will increase speculation about Labour MPs' concerns about the party's direction under leader Jeremy Corbyn.
But Mr Burnham insisted that his move should not be seen as a sign that he does not believe Labour can win the 2020 general election.
"Quite the opposite," he told the Guardian, claiming that Sadiq Khan's victory in the London mayoral race and Marvin Rees' win in Bristol could help shape the party's future.
"I think what we are going to see in politics is that Labour can gain strength from what's happening in the cities and in devolution and that's where some of the ideas that may shape the 2020 manifesto may come from: what's Sadiq's doing in London, what Marvin is doing in Bristol and hopefully, in time, what I'm doing here. That is where Labour will renew itself and come back stronger."
Mr Burnham was expected to formally launch his campaign in Manchester, but the appearance of @Andy4Manchester on Twitter - a renamed version of his old Labour leadership account - revealed his ambitions for the 2017 vote.
He told the Guardian that big Labour names should run for the powerful mayoral jobs created under the Government's devolution agenda.
"The mistake Labour made in Scotland was that when devolution came, we didn't field our biggest names and consequently it looked like we didn't take it seriously enough. We can't make that mistake again."
He added: "The biggest mistake would be to underplay (English devolution) and to carry on and say: 'Westminster's where it's at, that's where everything happens and you're not really a serious politician unless you're in Westminster'.
"I'm making a break with this thinking by announcing my candidacy for the mayor of Greater Manchester. I think I can do more for the people I care about, here, by being here rather than there, given this change. I am thinking that the time has come - Westminster has become a bit of an irrelevance for some people and we really need to change the way politics works."
Mr Burnham, a Liverpudlian, has been MP for Leigh in Greater Manchester since 2001 and hopes to take the job as mayor of the new combined authority, which forms a key part of Chancellor George Osborne's Northern Powerhouse agenda.
Former Labour MP Tony Lloyd is serving as the interim mayor of the combined authority until the first election for the role in 2017.
Mr Burnham's move comes after it emerged shadow cabinet minister Luciana Berger is considering running for the new "metro mayor" role in Liverpool.