Thousands of single parents in London are being "locked out" of work because of the high cost of childcare, a new study has revealed.
Charity Gingerbread said its research also showed that half of single parents in the capital are forced to borrow money to pay to have their children looked after while they work.
One in six single parents are under employed, while 4,500 will miss out on the Government's pledge of 30 hours of free childcare, said the report.
On average, a single parent in London will spend half their income, after housing costs, on a nursery place for a child under the age of two, said Gingerbread.
Childcare costs in the capital are over a third higher than other parts of the country, and the problem is not being addressed by the Government, it was warned.
Gingerbread called on London Mayoral candidates to commit to supporting its campaign to help parents find work.
Gingerbread chief executive Fiona Weir said: "Making childcare affordable is essential for supporting more single parents back into the jobs market and ensuring that it pays to work. Not least because work is still deemed to be the best route out of poverty.
"Our analysis shows that supporting single parents into work not only benefits families, but also the Exchequer. A 5% increase in single parents' employment rate could generate £436 million a year as a result of increased tax revenue and reduced benefits.
"This scheme would also provide a much-needed leg-up for the thousands of pre-school parents working in London.
"We're calling on Mayoral candidates to support Gingerbread's plan and plug a gap that's currently not being addressed by any level of government or agency."
Women quoted in Gingerbread's report included:
:: Liz from Greenwich: "If I want to go back to work full time I would I have to pay nursery costs but for me it's too expensive. It would cost me £1,580 per month, so I only paid for two days per week and will only be returning to work part-time. Even then I have had to borrow money from family, as it still costs me £700 per month."
:: Mila from Enfield: "I was considered a high-earner on £35,000 but because of London weighting I missed out on tax credits and other benefits. I've also had to look at other career options because of the fact that I previously worked in hospitality, where there's a complete lack of flexible hour roles."
:: Gwyneth from Wandsworth: "I've scaled back my hours to 20 hours per week because I know what financial implications of having to work 9-5 mean in terms of childcare. I also know that come the six-week school summer holidays I'm going to have to give up my job because I will not be able to afford the childcare costs."