Theresa May has been accused of “raiding the budgets” set aside by local authorities to help disadvantaged children in order to fund the government’s manifesto pledge to double the amount of free childcare for working families.

Local authorities currently receive government funds for 15 hours of free childcare for three- and four-year-olds. This will increase to 30 hours from next September.

Under the present system, local authorities have been able to pay extra cash to schools with nurseries from that budget because they employ qualified teachers and are disproportionately used by poorer families. They have also been able to set aside extra funds to ensure children from the most disadvantaged families get more than 15 free hours.

However, local authorities will now no longer be able to offer additional funding above a set hourly rate per child, it is claimed. Instead, there will be a requirement to pass on 95% of centrally provided funds directly to childcare providers. Those affected by the new policy will include 17 local authorities that now offer some of their families extra hours, including Wandsworth, Redcar, Surrey and Nottingham.

The new offer of 30 hours of free childcare, which was part of the Conservative manifesto at the general election, is available only to working families, so any child from an unemployed family currently getting more than 15 hours will lose that extra support. About 80% of three-year-olds from the most disadvantaged areas currently attend childcare with a qualified teacher or early years professional.

By preventing local authorities from paying “quality supplements” it is likely that schools will either need to reallocate funds from the main school budget or relegate the status of their school nursery.

Dr Kitty Stewart, associate professor of social policy at the London School of Economics, said the policy threatened to move cash away from disadvantaged children to pay for the childcare costs of better-off families. “The significance of these restrictions cannot be overstated,” she said. “I think it’s that they are desperately trying to deliver the 30 hours of free childcare pledge. They need more money, otherwise they can’t provide it, and are having to raid the budgets that are currently going to non-working families or those who are disadvantaged.”

Lucy PowellMP, chairwoman of the all-party group on nursery schools and nursery classes, said: “Investing in early years is not just about childcare for working parents, important as that is. It’s also critical to closing the education inequality gap that can already be very wide before children arrive at school.” A DfE spokesman said councils could still offer additional cash to child care providers from their wider budget. He said extra support for disadvantaged families was provided through universal credit and the pupil premium.