By Dominic Casciani BBC News Online community affairs reporter

Almost one in 10 children are severely, persistently poor

The fortunes of some of the poorest children in the UK may be worsened if their parents move from welfare into work, a report suggests.

A major study of 4,000 of the poorest British children throughout the 1990s has found a fifth of the worst-off families were those with adults in work rather than on benefits.

The report, by charity Save the Children, urges the government to develop more flexible benefits in order to hit its target to cut child poverty in half by 2010.

In 1999 the government said it was prioritising child poverty by introducing measures such as family tax credits.

Million in severe poverty

According to the charity, almost one in 10 British children experienced the worst forms of poverty during the 1990s - approximately one million children.

SEVERE CHILD POVERTY INDICATORS Below 40% of median British income entering child's household Children go without necessities such as three meals a day, a warm winter coat or own pair of shoes Parents go without at least two such necessities Source: Poverty and Social Exclusion Survey

But the report found children whose parents yo-yo between work and unemployment often live in worse conditions than those whose parents are constantly out of work.

Parents in short-term work could find themselves worse off because they suffered a dramatic fall in income - and a delay in benefits - once that job ended.

In a small number of cases families would actually have been less impoverished had the parents not tried to find jobs, the figures suggest.

Family instability

This constant switching between benefits and short-term jobs exacerbated family instability, income, housing security and general well-being, said the authors.

In turn, children suffered crises in confidence, were more likely to be bullied, missed out on activities others took for granted and went without basics such as warm winter coats, stout shoes and proper meals.

Sue Middleton, director of the Centre for Research in Social Policy and co-author of the report, said: "The government was right to take up child poverty as a major issue.

"But one of the main problems is where they experience change in their lives this can lead to severe poverty."

Ms Middleton said that if the UK wanted to have a flexible labour market, then it also needed a flexible benefits system.

"There is some evidence that a very few people might have been better off [not taking work]," said Ms Middleton.

"Our concern is whether the government can meet the targets without focusing on those in the most severe poverty."

Madeleine Terse, of Save the Children, said if the government wanted to tackle poverty, then it had to start with the poorest - and this may require more specific policies.

She called on ministers to look specifically at the Social Fund.

HAVE YOUR SAY What is needed is benefits to be phased out as earnings increase, gently going from receiving benefits to paying tax. Jonathan Kelk, UK Send us your comments

Introduced in 1988, the fund has long been opposed by child poverty campaigners.

It provides loans for essential basics such as fridges - but then reclaims the money by deducting it from benefits.

Furthermore, the fund is capped each year meaning that it can run out in some areas but not others.

Ms Terse said: "Clearly it is not working as it should be at present. The social fund can't cope with the level of demand and it is imposing additional debt."