The report by the London School of Economics (LSE) says 10% of Britain's children have not gained at all from general rises in living standards in recent years.

The research shows the government has a long way to go to fulfil its pledge to eradicate child poverty within a generation.

The Child Poverty Action Group says the problem can only be solved by increasing income tax.

One million children

Last week, Chancellor Gordon Brown asked child poverty experts for their advice on how to escalate the government's anti-poverty drive to lift an extra 200,000 children out of poverty by the middle of next year.

The government had already promised to raise the standard of living of 800,000 of the most disadvantaged children by the year 2000.

It says it has adopted a variety of different measures to achieve its aims, such as raising child benefit and its Sure Start programme, which targets children aged 0 to 4 living in deprived areas.

But the LSE report says "a large and sustained effort" is needed for many years.

Paul Gregg, a senior research fellow at the LSE, said: "They [government ministers] have got a long haul ahead of them. These are ambitious targets."

He added that years of cuts in benefits and in tax breaks for families had worsened the problem of child poverty.

"Child benefit has been declining, the old tax breaks are gone and child welfare payments are not rising. All that is dragging down families with children."

He said expensive childcare and an increase in poorly paid part-time work had also affected poverty.

Mr Gregg said unemployment was one of the main causes of poverty and that Britain had a third more families out of work than other developed countries.

Chancellor Gordon Brown has pledged to eradicate child poverty

In a fifth of households, there is no adult in work and only 40% of single parents work, compared with 80% in the rest of Europe.

He called for more support to be given to families and said raising benefits would not tackle the problem on its own.

"You have to get work into deprived communities," he said.

The government says this is exactly the aim of its welfare-to-work programmes that target single mothers, the young unemployed and those who have been out of work for some years.

It adds that it is introducing measures to ensure a wider range of childcare facilities and more parental support.

Research shows that poverty can have a dire effect on children's health and life chances.

Mothers-to-be in deprived areas, for example, are more likely to have premature babies, which can affect their future health.