George Osborne has been labelled the "downgraded Chancellor" and accused of being in "complete denial" over the loss of the UK's prized AAA credit rating.
Shadow chancellor Ed Balls claimed his opposite number was "just making it up as he goes along" and piled on the humiliation by reciting the Government's own words on the importance of the rating.
He told the Mr Osborne to get "out of denial" and come up with a new plan for jobs and growth.
"The downgrading of Britain's credit rating is, in this Chancellor's own words, humiliating for this Government," he told MPs.
But Mr Osborne, who arrived in the Commons chamber to answer an urgent question to chants of "resign" from the Labour benches, insisted the downgrade had not brought "excessive volatility" in the markets.
Ratings agency Moody's revised downward its verdict on the UK economy late on Friday, putting Mr Osborne under intense pressure. The Conservatives put the safeguarding of Britain's credit rating as the top benchmark to judge its economic success.
Mr Balls said: "The first economic test he set himself - now failed by this downgraded Chancellor. And yet he remains in denial, offering more of the same failing medicine when even Moody's now agree sluggish growth is the problem."
Mr Balls said the Chancellor must put the national interest before his own political pride.
He added: "He used to say a downgrade would be a disaster, today he says this downgrade doesn't matter - but he is still warning a further downgrade really would be a disaster.
"It is utterly baffling and illogical - he's just making it up as he goes along."