Left-winger Jeremy Corbyn has indicated he would seek to build a shadow cabinet drawn from all wings of the Labour Party if elected leader next month.
The signal comes after Mr Corbyn issued a plea for unity amid warnings that his election could split the party.
The Sunday Times reported that eight senior figures currently attending shadow cabinet - including leadership rivals Yvette Cooper and Liz Kendall, shadow chancellor Chris Leslie and shadow defence secretary Vernon Coaker - would refuse to serve under the veteran backbencher. One unnamed senior party figure told the paper Corbyn would struggle to field a complete team of shadow ministers.
But the Islington North MP said he was ready to offer a job to Ms Kendall and other Blairite MPs, telling The Observer: "Of course there are differences of opinion and I have to be big enough to accommodate those differences of opinion and I understand that.
"Some colleagues have said they would not be very keen on working with me, but I am sure these things were said in the heat of the moment."
Having come into the contest as the rank outsider, the veteran backbencher has become bookies' favourite after scooping the most nominations from constituency parties, though he insisted he was "cautious" about polls putting him out in front.
Ms Kendall accepted that Mr Corbyn was ahead in the race but insisted that "things will change" before the new leader is announced on September 12.
She is tomorrow due to unveil plans to tackle inequality - including £1 billion for pre-school support for children, paid for by reversing inheritance tax cuts - which she told The Observer would provide a "credible alternative of hope for the future".
While party members were "desperate for an alternative to where we have been for the last five years", many of Mr Corbyn's new supporters were not old enough to remember that his kind of politics repeatedly lost Labour elections in the 1980s, she said, adding: "Jeremy Corbyn does not have a monopoly on hope or a monopoly on setting out an alternative."
Fellow candidate Andy Burnham questioned whether Mr Corbyn's anti-austerity agenda was "affordable, deliverable, credible".
Mr Burnham - who has won the endorsement of former leader Lord (Neil) Kinnock - will this week launch a manifesto which he said would offer a "big vision" along with a "careful" plan for how it can be delivered.
He told the Sunday Express that Mr Corbyn had "connected" with party members who want a change from the "retail politics" of recent years, but added: "My pitch is that I want that change too, but that doesn't necessarily mean a change of political direction left or right. I think it is about a change in style to the way Labour is doing politics."
Central to his policy agenda will be a combined health and social care service within the NHS, which would protect older people from losing their homes and savings to the cost of care late in life.
Lord Kinnock hailed Mr Burnham for his ability to "attract votes from the breadth of the British people" and warned Corbyn backers that "it won't be enough" for Labour to become a party of protest.
Announcing his endorsement in an article for The Observer, Lord Kinnock said: "In the leadership election, we are not choosing the chair of a discussion group who can preside over two years or more of fascinating debate while the Tories play hell with cuts. We have to elect a leader capable of taking us to victory in the 2020 election and of being a Labour prime minister."
The former Labour leader warned that figures from the "Trotskyite left and the Telegraph right" were backing the veteran left-winger for "their own malign purposes", after Labour introduced new rules allowing anyone paying a £3 registration fee to vote in the leadership election.
But Mr Corbyn dismissed warnings of "entryism" by mischief-makers as "absolute nonsense", insisting the new registered supporters were "people who are serious about their politics and want the Labour party to be able to represent them and ... have felt rather unrepresented in the past years".
Former Coventry South MP Dave Nellist, who was expelled from Labour in 1991 over his links to the far-left Militant group and now chairs the Trade Unionist and Socialist Coalition, said that Mr Corbyn would need "a new party" if he is elected and recommits Labour to policies abandoned under Tony Blair.
Mr Nellist told the Independent on Sunday: ""Jeremy will be a prisoner inside the parliamentary party. More than 90% of them won't be on his side. Labour's annual conference will be weeks away. That won't be enough.
"He'll need to make an urgent call for a larger gathering where every organisation on Britain's left should be invited to debate what happens next."