Jeremy Corbyn has said George Osborne should be "considering his position" as ministers prepare formally to ditch cuts to benefits for the disabled set out in his Budget .
The Labour leader urged the Chancellor to come to the House of Commons and explain how he will "reconfigure" his spending plans in the wake of Iain Duncan Smith's dramatic resignation over welfare cuts.
It is understood that new Work and Pensions Secretary Stephen Crabb will tell MPs in a statement that the curbs to the Personal Independence Payment (PIP) have been abandoned.
And Prime Minister David Cameron is expected to mount a defence of his Government's record when he appears in the Commons to report back from last week's EU migration summit amid headlines talking of "civil war" in the Conservative Party.
Cabinet minister Greg Clark issued a plea for Conservatives to "come together again" and to avoid "scrapping". The Communities Secretary said Mr Duncan Smith had been working "hand in hand" with Mr Cameron and Mr Osborne on the welfare changes.
"I don't think it should be civil war at all because actually Iain and the Prime Minister and the Chancellor have worked very successfully together over the years, for example, to get more people into work than ever before, to have fewer children in workless households," Mr Clark told ITV's Good Morning Britain. "We need to come together again to continue that important work."
Mr Corbyn said Mr Osborne should scrap cuts in corporation tax and capital gains tax announced in the Budget in order to fill a £4 billion gap left by the PIP climbdown.
The Labour leader told BBC1's Breakfast that the reversal of the Government's welfare plan amounted to "the biggest U-turn for a very long time".
He said: "The Budget doesn't add up. The Chancellor of the Exchequer should come back to Parliament and explain that.
"Far from just Iain Duncan Smith resigning, if a Chancellor puts forward a Budget - as he did - knowing full well that he is making this huge hit on the disabled, then really it should perhaps be him who should be considering his position.
"His Budget simply doesn't add up and it unravelled within hours of him presenting it. This isn't the first time a George Osborne Budget has unravelled.
"It seems to me we need to look at the very heart of this Government, at its incompetence, at the way it puts forward proposals that simply don't add up and expects the most needy in our society to take the hit for them."
Mr Clark confirmed the Government will "take a step back and review" the proposed reduction in PIP payments saying: "Clearly a lot of people feel that it needs to be looked at more closely before it's implemented."
He said the new Work and Pensions Secretary will continue the "progressive agenda" set by Mr Duncan Smith on issues like the introduction of the Universal Credit to replace a range of benefits.
He said he regretted Mr Duncan Smith's resignation but rejected his claim that the Government was undermining its "one nation" ambitions by balancing the books on the back of the working age poor and vulnerable.
"I disagree with Iain about that," said Mr Clark. "He has clearly got frustrated over this particular issue but over six years he has taken his very progressive agenda into government with great success in partnership with the Chancellor and the Prime Minister.
"I hope that, as things settle down, Iain will recognise that the best hope for continuing this progress we've made is by us all coming together. There's no point in scrapping with each other when we've got an important job to do of making sure that not only is the economy heading in the right direction but every part of society is benefiting from it."