Around two-thirds of mothers say the cost of childcare is an obstacle to them working more, according to a survey by MumsNet and the independent thinktank the Resolution Foundation.
The survey of 2,000 mothers found that 67% of those in work and 64% of those not in work say the high cost of childcare is a barrier to taking on more employment. The findings underline the likelihood that politicians will make greater help with childcare a big part of their manifesto pledges at the next election.
There are growing signs that Labour has decided to make a long-term commitment to universal free childcare one of its two or three most important proposals. The commitment might take more than two parliaments to meet, but these figures underline that childcare is a barrier to full employment.
Nick Clegg, the Lib Dem leader, has battled to make childcare one of his central issues, but he has had differences within the coalition over the extent of deregulation within the childcare sector.
Well over a third (37%) of stay-at-home mothers say they would like to work and would hope to do an average of 23 hours a week. And 20% of mothers who are already employed would like to take on an extra 10 hours a week on average.
Among mothers who are already working, it is those on lower earnings who are more likely to want to take on more hours. The average earnings of those who would like to work more, at approximately £13,000 a year, are less than half those who would not, at approximately £29,000.
The results come from a survey of nearly 2,000 mothers with children under 10. Respondents were asked about their family makeup, income, childcare arrangements, work preferences and the barriers to work created by childcare, as well as how some of these might change under a different system of childcare support.
The report also analyses OECD data to show that the UK lags behind some other western economies on rates of maternal employment, with about 67% of mothers in some form of paid work - compared with 86% in the best performer, Slovenia, and behind Iceland, Sweden, Denmark, the Netherlands and Finland.
The Resolution Foundation says this relatively low employment rate is a concern, particularly for lower income households, because the risk of poverty for children in families with only one earner is much higher than for those in dual-earner families. There are approximately 5.5 million working mothers of dependent children across the UK, and 2.9 million mothers who do not work.
The report's other findings include:
• Childcare costs are named as the biggest single obstacle to more work by more than four in 10 mothers (42% of those in work and 41% of those not working).
• For working mothers, the next most common barrier to more work is employers being unable or unwilling to offer more hours (cited by 17%).
• Nations with the best maternal employment rates are more likely than UK employers to offer flexible work options, including the ability to set some of your own hours or to use accumulated hours to earn leave days.
Justine Roberts, CEO of Mumsnet, said: "Cost of childcare is clearly proving a real barrier to women working. It's time to start thinking of childcare as infrastructure to the economy in the same way as we think about transport or technology. Enabling women who want to work or who want to work more hours to do so brings real financial benefits to their own family income and also to the wider economy."
The current entitlement to free childcare is 15 hours a week for all parents of children aged three and four. The government is planning a scheme to offer extra support to working parents with younger children, including a tax-free voucher system allowing most better-off parents to claim up to £1,200 towards the cost of looking after a child.