Many poor families have sole earner
Nearly a third of families living in poverty have a "traditional" sole breadwinner set-up, according to research.
Some 400,000 couples where only one parent earns have been struggling on less than £251 a week, figures compiled by NatCen for the Joseph Rowntree Foundation (JRF) show.
Double-income families made up 16% of the 1.3 million classed as in poverty, while 105,000 were headed by single parents who work, and the rest did not have anyone earning.
NatCen examined data from the Family Resources Survey conducted in 2009-10 and 2010-11.
Katie Schmuecker, policy and research manager at JRF, said: "The traditional family model where one parent - usually dad - goes out to work and supports his family does not offer a guaranteed route out of poverty in Britain today.
"Our low pay jobs market means many families that are reliant on a single breadwinner find it hard to make ends meet.
"Measures like the Living Wage, supporting people to progress into better jobs and ensuring it always pays to work more will all help increase household incomes.
"So too will helping more families to become dual-earning households. This means we have to tackle the barriers that prevent people that want to work from doing so - such as unaffordable childcare and the lack of financial incentive to work.
"Otherwise many parents and their children may find themselves trapped in poverty with little prospect of bettering their situation."
The ippr think-tank called for second earners to be allowed to keep more of their pay before means-tested benefits are withdrawn.
Kayte Lawton, senior research fellow, warned that under Universal Credit, as soon as a second earner entered work, 65p of every £1 earned would be lost to withdrawn benefits.
"Many fathers work long hours, making it harder for them get involved in family life and more difficult for more mothers in poorer families to work," she said.
"Childcare enables parents with young children to work, particularly mothers, but remains expensive for many poor families and needs to be made more affordable."
Laura Perrins, spokeswoman for campaign group Mothers At Home Matter, said: "This is what Mothers At Home Matter have been saying for many years.
"The report proposes a packet of measures which centre around the second earner returning to work. If JRF recommendations were followed through then it suggests the right of families to care for their children at home, is not one which low-income families can have, and should be preserve only of the wealthy.
"We at Mothers At Home Matter believe that all families should have at least the choice to care for their children at home, particularly when the children are very young.
"Claiming that you are helping low-income, single-earning couples by forcing them to use childcare and turning them into dual-earning families is not a solution that recognises the desire of these families to care for their children at home. Many families have already decided that childcare is not yet in their children's best interests.
"Low-income families often do have a mum working part-time, but they do not always use external, paid for non-family childcare. They are more likely to rely on family or friends to care for children, or the part-time work is completed during schools hours as these families want to be there for their children after school."