Jeremy Corbyn will face a "bumpy ride" as Labour leader as major policy divisions emerged within his newly-appointed senior team, a shadow cabinet minister has acknowledged.
The new leader is already facing a backlash within Labour ranks after appointing one of his most hardline left-wing allies as shadow chancellor.
Serial rebel John McDonnell has been handed the crucial task of overseeing the party's economic policy in a team that Mr Corbyn's aides described as "refreshing" and "dynamic".
Former leadership rival Andy Burnham has accepted a job as shadow home secretary, although a host of significant players have refused to take on frontbench roles. There has also been criticism that no women are in the most senior positions.
Mr McDonnell dismissed claims women had been snubbed for the top jobs and insisted the health and education portfolios - which have gone to Heidi Alexander and Lucy Powell - are more important than the great offices of state.
He told Sky News: "For most people the real top jobs are the ones that provide the services like health and education, those sorts of things. So he has broken with that tradition and I'm really pleased."
He added: "You can't say that Foreign Secretary is more important than delivering education to our children, or the health of the people of this population.
"You'll see in future that the person responsible for education or health and those concrete services will be the people who will be out there arguing the policies. And in fact in some ways the Chancellor of the Exchequer will play less of a role because it will be the people who are really delivering the real services."
The scale of the problems Mr Corbyn faces in uniting the party were underlined as Hilary Benn, who is staying on a shadow foreign secretary, declined to offer full endorsement for Mr McDonnell's appointment.
And the new shadow leader of the House of Commons Chris Bryant revealed he had turned down the defence portfolio because of "profound" disagreements with Mr Corbyn on policy.
Asked if he was 100% behind Mr McDonnell being handed the key economic job, Mr Benn told BBC Radio 4's Today programme: "This is the choice that Jeremy has made. I respect the choice that Jeremy has made as leader.
"We have just come off the back of two bad election defeats for the Labour Party, and our principle task is to win the people's trust when it comes to the economy.
"John's first and last task as shadow chancellor will be to win the trust and confidence of the British people in arguing for a different economic policy."
Pressed on whether he welcomes Mr McDonnell taking charge of the Treasury brief, Mr Benn said: "I welcome everybody who is serving in Jeremy Corbyn's cabinet... because Jeremy won a thumping victory, we have a responsibility to rally round him."
Mr Benn attempted to calm fears among many Labour MPs that Mr Corbyn could campaign for Britain to leave the EU in the in/out referendum expected next year.
Chuka Umunna stood down as shadow business secretary complaining the new leader had refused to give him an assurance he would not back a "Brexit" vote.
But Mr Benn said: "Jeremy said whatever differences we may have with some aspects of European policy and whatever reforms we want to see, we will stay to fight together for a better Europe."
Explaining his decision to turn down the defence job, Mr Bryant said: "I think Jeremy needs somebody in that particular portfolio where he and that person are rather more at one than I could be."
Mr Corbyn opposes the replacement of the Trident nuclear weapons system and has questioned the role of Nato.
Mr Bryant said: "It's difficult and I think it is going to be a bit of a bumpy ride because there are issues on which - they are not light issues - I profoundly disagree with him, like on Nato, Russia and things like that."
Labour MP Diana Johnson, a former frontbencher, is among those condemning the "old fashioned male-dominated Labour politics" of the reshuffle.
In an apparent effort to head off criticism, Labour officials followed up an announcement that Angela Eagle was taking the business brief with news some hours later that she would also be shadow first secretary of state, taking on Chancellor George Osborne at the weekly PMQs sessions when David Cameron is away.
Seema Malhotra will be Mr McDonnell's number two as shadow chief secretary and Rosie Winterton remains chief whip.
But Caroline Flint became the latest senior figure to refuse to serve under Mr Corbyn, claiming "I can best support the Labour Party and the leadership from outside the shadow cabinet" but stressing "I remain loyal to the Labour Party and will do everything I can to help us win the next general election in 2020".
Mr Corbyn was declared Ed Miliband's successor on Saturday on the back of a surge of support from activists that saw him attract a massive 59.5% of votes - topping the ballot among party members as well as trade unionists and new supporters.
He is expected to make his first appearance on the Commons frontbench of his entire 32-year career as an MP later as he leads the party in opposing the Government's anti-strike laws.