An overall cap on welfare spending has passed the Commons by a huge majority of almost 500, despite warnings it could push hundreds of thousands of children into poverty.
During the MPs' debate on Chancellor George Osborne's plans, Labour's Diane Abbott warned both the Government and her own side not to play politics with people's lives.
But Mr Osborne's Charter for Budget Responsibility was passed 520 to 23, majority 497, as the main parties largely united to back the plan.
Including two tellers, 13 Labour MPs opposed the scheme, fewer than predicted, with the remaining no votes being made up of minor parties.
At the Budget, Mr Osborne set the cap level for the first four years, rising in line with inflation from £119.5 billion in 2015/16 to £122 billion in 2016/17, £124.6 billion in 2017/18 and £126.7 billion in 2018/19.
The figures are in line with forecast levels of welfare spending under current policies.
Speaking in the wake of the vote, Matthew Reed, chief executive of The Children's Society, said: "Today's cross-party support for capping welfare is a betrayal of their commitment to end child poverty.
"It risks pushing more children into poverty by tying government's hands, making it harder to make sure the most vulnerable families and children get the support they need to cope with rocketing rents, rising childcare costs and soaring fuel prices.
"Independent experts estimate that by 2020, 800,000 more children will be living in poverty if the government continues with its current policies.
"Capping welfare risks derailing all three parties' commitment to end child poverty and will harm the children whose futures they are supposed to protect."
Will Higham, director of UK poverty at Save the Children, said: "Children have already paid the highest price in the recession.
"It is all well and good to look towards a recovery, but parties that vote in favour of the cap need to spell out urgently what provisions they will make to ensure that the poorest children do not get forgotten about and left behind.
"Parties need to explain how they will work to improve wages and welfare to ensure that work pays.
"Otherwise, today's vote will become a straitjacket, binding future governments from taking action to stem a rising tide of child poverty."
PCS union general secretary Mark Serwotka said: "The welfare cap is not a solution to anything, it is a gimmick, and a very nasty and dangerous one that will cruelly punish vulnerable people whose lives depend on the support benefits and tax credits provide.
"With tens of billions of pounds lost every year through corporate tax avoidance, MPs should hang their heads in shame that they are voting for a cap that risks driving more people into poverty and putting more families on the streets."
In the Commons, the Chancellor defended the coalition's reforms as vital to bringing fairness back into the welfare system.
He said: "(Under the system we inherited) it was not fair benefits were unlimited, we have introduced a cap.
"It wasn't fair those looking for work faced marginal tax rates as high as 96%, sapping the incentives to find a job.
"We are addressing that through universal credit.
"Not fair: that was the welfare system we inherited.
"Unfair to those trapped in poverty, unfair to the millions of people who paid for it.
"It is a perverse distortion of what (welfare pioneer) William Beveridge had conceived and in the face of opposition to each and every measure we have introduced, we are removing those distortions, restoring the work incentives and creating a fair welfare state."
Mr Osborne said there was no reason in principle for welfare not to have a fixed budget in the same way as spending at the Home Office or the Ministry of Defence.
And the Chancellor added: "Some of these benefits have relatively stable and predictable costs, like statutory maternity pay, others like housing benefit have consistently grown much faster than forecast.
"But each one involves hundreds of millions, often billions, of pounds of spending and deserves the same careful management and scrutiny... some of these benefits help some of the most vulnerable citizens, like Disability Living Allowance, but that is not an excuse for the failure to manage its budget.
"After all, our NHS also cares for the most vulnerable and yet that doesn't stop us from giving the NHS an annual budget."
Shadow chancellor Ed Balls said: "We support capping social security spending, a policy the Leader of the Opposition (Ed Miliband) advocated last year, and with welfare spending now £13 billion higher than the Government planned in its spending review, Labour will make different and fairer choices to get the social security bill under control and tackle the root causes of rising spending."
Speaking during the backbench portion of the debate, Ms Abbott said: "This is not a game, this is about people's lives, whether it's elderly people who are dependent on some of the age-related benefits which will fall under the cap, whether it is the disabled, whether it is people in low-paid work that depend on the system of tax credits.
"This is not a game, this is people's lives.
"And if it is really the position of members opposite that poor people should be made to live on even less, they should at least have the grace to be dignified about it and they should not turn it into a game."