Former Home Secretary Alan Johnson has backed one of the Labour party's few MPs in the south of England to be the party's deputy leader.
Mr Johnson endorsement of Ben Bradshaw, MP for Exeter in Devon, is a coup given the former Cabinet minister's popularity in the party.
Mr Bradshaw has also received backing from Labour council bosses in the south of England, it emerged.
The backing comes as current deputy leader Harriet Harman conceded even some Labour voters were "relieved" the party did not sweep to power.
Speaking to The Huffington Post, Mr Bradshaw, a former Cabinet minister, echoed her point that the party failed to exploit uncertainty about the Conservatives.
He said: "A lot of people wanted to vote Labour, they weren't enthusiastic for the Tories, but they didn't trust us on the economy or have enough confidence in our leadership."
In his endorsement, Mr Johnson said Mr Bradshaw "has always been a brave and rational voice within the Labour Party".
He added: "He is also a brilliant communicator. I worked with Ben and I know just how assiduous, energetic and hard-working he is. These are the qualities we need in a deputy leader."
Mr Bradshaw, a former BBC journalist viewed as being from the Blairite wing of the party, is the only Labour MP in either of the leader or deputy leader contests who represents a southern seat outside the capital.
His central campaign message is Labour needs to appeal to voters beyond its heartlands if it is to win a general election.
Mr Bradshaw's rivals to replace Ms Harman are Rushanara Ali, MP for Bethnal Green and Bow in London, Stella Creasy, who represents Walthamstow in London, Angela Eagle, MP for Wallasey in Merseyside, John Healey, MP for Wentworth and Dearne in Yorkshire, and West Bromwich's Tom Watson from the Midlands.
Mr Bradshaw said: "I am delighted to have Alan's support. He is one of our most popular, respected and best loved politician, someone with the ability to reach out within but also well beyond the Labour family.
"This is what our new leadership team are going to have to do, if we're to have a hope of winning the next election."
Meanwhile, council leaders and party group bosses from Kent, Essex, Southampton, Sussex, Gloucestershire, Somerset, Plymouth, Devon and Cornwall have endorsed Mr Bradshaw against concerns the party is too focussed on winning support in the north, London and Wales.
In a letter to Labour MPs, they write that the party has to look beyond its heartlands to voters "who might have voted Labour but who chose not to do so this time".
The letter in support reads: "If we are to build Labour's presence across our regions in order to provide more fertile ground at the next General Election, it is imperative that the Labour Party listens to the voices of people who campaigned hard across our regions for a Labour victory, alongside the views of residents who voted Labour, and also of those people who might have voted Labour but who chose not to do so this time.
"With the geographic make-up of the Parliamentary Labour Party now predominantly focused around the North of England, Wales and London, it is essential that the ongoing Leader and Deputy Leader campaigns are representative of the whole country.
"In order to ensure that our voices are heard, we are calling on the Parliamentary Labour Party to ensure that Rt Hon Ben Bradshaw MP gains the nominations needed to see him on the ballot for Deputy Leader.
"Since 1997 Ben has held Exeter, a previously safe Tory constituency, for Labour and in fact nearly trebled his majority to over 7000 at this election, bucking the national trend. He has done this in partnership with a Labour Council in Exeter, and we know from colleagues there that he values the contribution that Labour in Local Government can and does make.
"Ben’s successful record of effective campaign organisation, built on an aspirational message for the success of everyone in the City of Exeter, and allied to his hard work as a Constituency MP means that he has the experience, the knowledge and the long-term vision that will be vital in the upcoming debate on the future direction of the Labour Party."
Mr Bradshaw told The Huffington Post Uk: "We face a huge challenge across the three southern regions of England, where we hold just 12 of the 197 parliamentary seats.
"A lot of people wanted to vote Labour, they weren't enthusiastic for the Tories, but they didn't trust us on the economy or have enough confidence in our leadership.
"If we are to be a truly national party, we must reconnect with voters across the South and elsewhere, where we must win back support from the Conservatives."