Some families are being denied access to free nursery education unless they agree to pay compulsory "top-up fees" for extra hours, a cross-party group of MPs has warned.
The practice risks excluding poorer families from nurseries, according to the Commons Public Accounts Committee (PAC) which called for the Department for Education (DfE) to tackle the issue.
Under the current system, three and four-year-olds are entitled to 15 hours of government-funded nursery education each week. But a new PAC report raises concerns that some families are being told they are eligible only if they pay for additional hours.
"We are concerned that some providers may be excluding families which do not pay for additional hours," the report says. "In the department's own survey of parents, some parents stated that they could not receive the 'free' entitlement without buying additional hours.
"One witness suggested that compulsory top-up fees were commonplace in some nurseries and we have seen other evidence of parents being asked for further payments. Such practices risk excluding poorer families from nurseries."
The report, examining free nursery education for pre-schoolers, commended the DfE for increasing early years education - more than 800,000 three and four-year-olds now get the free hours. But it warned that the DfE has a "limited understanding" of how the £1.9 billion funding is spent, and says the Government should collect and publish this information.
The report also raised concerns that poorer families are the least likely to take advantage of free nursery education, with a 9% take-up between these families and others. And it warned that evidence of the long-term benefits of nursery education was "questionable".
PAC chairwoman Margaret Hodge said: "High-quality early years education can have lasting benefits for children and results at age five have improved. But the department needs to get to grips with why there is little improvement at the age of seven and what happens between five and seven to lessen the effect."
She added: "It is unacceptable for any parent to be charged for what should be a free entitlement. It is also completely unacceptable that some parents cannot access the free education unless they agree to pay 'top-up' fees for more hours. The Department must take action to prevent this."
A DfE spokeswoman said: "We will continue to investigate and pursue any cases where parents are required to pay for their child's free nursery place with the local authority - who have a duty in law to make sure that places are free of charge."