The government has missed the first target in its bid to end child poverty.
The target of lifting 1m children out of poverty has not been met
Tony Blair pledged in 1999 to eradicate child poverty by 2020 - and to have cut it from 4.1m to 3.1m by April 2005.
Department for Work and Pension figures show the number of children in poverty has fallen by 700,000 since 1999, missing the target by 300,000.
Ministers say the government remains committed to wiping out poverty within a generation, but opposition MPs called it "disappointing" and "disturbing".
A family is considered to be officially poor if they are living on less than 60% of Britain's median (average) level of household income.
This means a single person is currently judged to be living in poverty if they have an income of less than £100 per week, said Peter Kenway from the New Policy Institute think tank.
He said a household of two adults with two children was living in poverty if it had a weekly income of less than £260.
DEFINITION OF POVERTY
Anyone living on less than 60% of the UK average (median) income
For a single person it means an income of less than £100 per week after tax, housing costs and benefits, says the New Policy Institute
For a family of two adults and two pre-school children it means living on a weekly income less than £260, says the institute
Poverty campaigners say good progress has been made but they want further investment in benefits schemes to help lift more families above the breadline.
Shadow work and pensions secretary Philip Hammond said: "These figures are further proof that, despite the progress that has been made, the state alone cannot eradicate child poverty.
"We must employ the skills of the private, voluntary and social enterprise sectors to create opportunities for parents who are struggling to get back into work."
David Laws MP, Liberal Democrat Shadow Work and Pensions Secretary, said the figures were "extremely disturbing" and called for an urgent review of the child poverty target.
"It is no surprise the Government is failing to deliver when the CSA is in chaos, tax credits are a mess and our lone parents employment rate is one of the lowest in Europe," he said.
POVERTY 1996-97 TO 2004-05
Total number of people in absolute poverty cut by 7.1 million to 3.1 million
Pensioners in absolute poverty down by 2.1 million to 700,000
Children in absolute poverty down by 2.4 million to 1.9 million
Figures take housing costs into account
Source: Department for Work and Pensions
Employment Minister Margaret Hodge told the BBC the government was committed to its pledge to eradicate child poverty within a generation, but she acknowledged that a lot of work remained to be done.
"Of course we've got to constantly renew our thinking. Of course we've got to redouble our efforts," she said.
"But you - three or four years ago - probably would never have thought we'd get this far. And we've set ourselves deliberately tough targets so that we really do drive forward policy and have a real change for children and their families".
Labour MP and former social security minister Frank Field said: "The target is audacious but it is not achievable.
"I was amazed and gobsmacked when the government announced it."
Mr Field added that "braver" ideas were needed to alleviate child poverty.
Under the government's welfare-to-work policies, more than 300,000 extra lone mothers have found employment. But campaigners believe these strategies have left behind large families or those with disabled children.
Guy Palmer from the New Policy Institute said he thought the target set was right, calling it "challenging but achievable". The government should "redouble their efforts", he added.
Charity One Parent Families said the government had set itself "a historic and laudable task" to reduce and eventually eliminate child poverty, and serious progress had been made.
Earlier Sir Jeremy Beecham, vice-chairman of the Local Government Association, said there had been a significant reduction in child poverty but there was "still much to be done".
He said enhancing the take-up of council tax benefit by the low paid would help reduce poverty numbers further.