The expanded childcare plan will see working families in England with three and four-year-old children receive an extra 15 hours a week of free childcare to a total of 30 hours from September.

However, National Day Nurseries Association’s (NDNA) annual survey found that just 44% of school nurseries are likely to offer 30 hours and a fifth said they are unlikely to, or definitely won’t.

More than a third (35%) said they still don’t know, five months ahead of the rollout.

NDNA said this means around 50,000 children, the equivalent of all pre-school three and four-year-olds in the whole of Greater Manchester, will be left without places so they’re missing out on £250m worth of childcare. But as many nurseries are still unsure, these figures could be higher.

It said this could be a huge blow to the government’s expanded childcare plans as full daycare is the largest part of the nursery sector which are best-placed to serve parents in 9-5 type jobs.

Purnima Tanuku, chief executive of NDNA, said: “There is no such thing as ‘free’ childcare – parents, nurseries and their staff are all paying for this.

“It is time the government stopped promising parents ‘free’ childcare hours unless they are prepared to invest the money needed. This manifesto promise is in real danger of failure.”

Tanuku said the survey shows plummeting confidence in the nursery sector and fears about sustainability at a time when many are faced with inadequate funding, soaring costs and recruitment problems.

The survey revealed 85% of nurseries are underfunded, with the average loss per child per year at £958 for 15 hours funded childcare. Increasing staff wages is the single biggest challenge nurseries face, with payrolls due to rise by a further 7% on average, meaning more are turning to recruit younger, less qualified staff.

“The government is relying on the private and voluntary sector to meet expected high demand. If there is no more money, the Department for Education (DfE) needs to give nurseries more flexibility in delivering these places,” said Tanuku.

“This includes allowing them to make mandatory charges to parents for extras over and above childcare, such as meals, activities and trips out. The DfE acknowledges that nurseries will need to make optional charges, but you can’t run a sustainable nursery business on voluntary charges.

“Without this lifeline, the policy will not be a success for all those who are entitled to it and nurseries fear they will get into financial difficulties and could even go out of business.”

Tanuku said that if the government can’t afford to do this, it should seriously rethink the childcare policy or delay the full roll-out for in-depth analysis to be done.

“Rather than forcing through this policy at the expense of quality and nursery sustainability, we strongly urge the government to listen to the sector which says nurseries cannot afford to deliver this in its current form.”