Iain Duncan Smith has delivered a devastating attack on the Government's austerity drive, accusing David Cameron and George Osborne of balancing the books on the backs of struggling working people and the vulnerable.
As Tory infighting spiralled out of control in the wake of his dramatic resignation, the former work and pensions secretary condemned the Chancellor's "arbitrary" cap on welfare spending and obsession with "short term savings".
Energy Secretary Amber Rudd immediately lashed out at Mr Duncan Smith's "high moral tone" and dismissed the critique as "completely wrong". Meanwhile, ministers at his old department clashed openly after pensions minister Baroness Altmann accused him of causing "maximum damage" in order to get Britain out of the EU.
Speaking on the BBC's Andrew Marr show, the former Conservative leader insisted his decision to quit was not "personal" or a "secondary attack" on the Prime Minister.
He said he felt the Conservatives were abandoning their "One Nation" approach and his position had become "impossible" amid "massive pressure" to finalise deep cuts to Personal Independence Payments (PIP) for the Budget.
Mr Duncan Smith said he finally chose to go after finding out that Mr Osborne had "juxtaposed" the £1.3 billion a year PIP curbs with tax cuts for the better off.
"I am concerned that this government that I want to succeed is not actually able to do the kind of things that it should because it has become too focused on narrowly getting the deficit down without being able to say where that should fall, other than simply on those who I think progressively can less afford to have that fall on them," he said.
"The truth is yes, we need to get the deficit down, but we need to make sure we widen the scope of where we look to get that deficit down and not just narrow it down on working age benefits
"Because otherwise it just looks like we see this as a pot of money, that it doesn't matter because they don't vote for us."
Asked why he decided to go even though the Treasury had signalled a last-minute climbdown on the PIP issue, Mr Duncan Smith said the department would still have been forced to find equivalent savings.
"It is a very peculiar way to try to set policy against a media agenda where you start Friday morning absolutely saying to everybody you must go out and defend it and then by Friday evening you are drifting away from it and then later on Friday evening somehow you say we have kicked it into the long grass," he said.
"The money required from the DWP still sits in the (Budget) Red Book. It will be a requirement that will bear down on working age benefits and that is the problem that I have."
Mr Duncan Smith said he had to consider whether the "compromises" of being in government "benefit or damage society".
He said he considered resigning a year ago after a series of spats with the Chancellor over cuts to tax credits and his flagship Universal Credit project, which is merging working age benefits and aims to ensure people are always better off in work.
"This has been a long running problem when I have felt really semi-detached in a sense, isolated more often in these debates because I am not able to convince people that what we were losing progressively ... was the narrative that the Conservative Party was this one nation party caring about those who don't even necessarily vote for it, who may never vote for it," he said.
Mr Duncan Smith said he became "progressively more and more depressed" about the Treasury's insistence on an "arbitrary Budget agenda which has a welfare cap in it". Too often policies were driven by "demands for short term savings all the time when things don't go right with the forecast".
"My point really was we shouldn't be debating (welfare cuts) in the context of just being above a welfare cap, which was an arbitrary position," he insisted.
"We should be discussing it in terms of how could we get the best aid to the people who most need it and then work from there as to how those changes came."
He added: "I sat silently in the morning of the Budget presentation because I then realised the full state of what was actually happening with regard to both the tax cuts and the juxtaposing (of PIP cuts) in the Budget."
Mr Duncan Smith said he had not been present at the Budget Speech as he was attending a funeral. "It gave me time to think about this," he added.
The ex-minister highlighted the Government's "triple lock" on the state pension - which means it increases in line with the highest of average wages, RPI inflation or 2.5%.
"My deep concern has been that this very limited narrow attack on what is working age benefits means we simply don't get that balance. We lose the balance of the generations. We have a triple lock on pensions which I was proud to do six years ago but with inflation running at 0% we really need to look at things like this," he said.
Mr Duncan Smith said the Government had already stripped £33 billion out of working age benefits.
And he flatly denied that his decision had anything to do with personal animosity to Mr Osborne or his desire for Britain to leave the EU.
"Don't doubt my motive on this. I am not about seeing the PM depart, because if there were a vote tomorrow I would vote for him. I want the team to succeed as a one nation team," he said.
Asked whether he thought Mr Osborne would make a good Prime Minister, Mr Duncan Smith said: "If he was to stand and if he was elected by the electorate, which is not just me it is everybody else, I would hope that he would.
"I think the same for almost everybody else. I have no view about anybody to be Prime Minister because the Prime Minister is there at the moment."
Ms Rudd told Sky News' Murnaghan programme she had "respect" for Mr Duncan Smith but his behaviour was "really disappointing".
"I do resent his high moral tone on that when the rest of us are absolutely committed to a one nation government," she said. "I do find his manner and his approach really disappointing."
Lady Altmann accused her old boss of "shocking" behaviour and trying to inflict "maximum damage" on the party leadership to get Britain out of the EU.
"Having worked alongside him as a minister in the Department for Work and Pensions (DWP), I have seen that he championed the very package of reforms to disability benefits he now says is the reason he has resigned," she said.
"I simply cannot understand why he suddenly chose to quit like this when it was clear that Number 10 and the Treasury had told him they were going to pause and rethink these measures. I'm particularly saddened that this really seems to be about the European referendum campaign rather than about DWP policy."
Lady Altmann said she had been "silenced" by Mr Duncan Smith for months and was "horrified" to see him "abuse the freedom to take sides the Prime Minister has generously offered to ministers".
"He seems to want to do maximum damage to the party leadership in order to further his campaign to try to get Britain to leave the EU," she added.
But fellow ministers Priti Patel, Justin Tomlinson and Shailesh Vara lined up to hit back at Lady Altmann.
Employment minister Ms Patel said: "Iain has always provided support and encouragement in all aspects of my work in DWP. All meetings with our ministerial team have been constructive and every minister has had the freedom to take forward policy ideas in their brief, to lead media campaigns and engage freely with parliamentary colleagues."
Minister for the disabled Mr Tomlinson added: "Iain has always conducted himself in a professional, dedicated and determined manner. He actively encouraged ministers and teams to engage, challenge and develop ideas."
Mr Vara added: "I have to say I'm surprised by Ros's comments. The fact is that I recall Ros attending all the meetings at which we openly discussed government policy and then we both went out to defend the policy in the Commons and Lords, which as you know wasn't always easy to do."
A source close to Mr Duncan Smith said Lady Altmann was following the "Downing Street script" by suggesting he was motivated by his desire for Brexit.
Labour ratcheted up the pressure on Mr Osborne amid the escalating rows, insisting he now had to "rip up" his Budget and "start again" when he comes to the House of Commons this week.