State primary schools are pressurising parents to withdraw their children from private nurseries and instead to bring them to reception classes at the age of four.
Parents of four-year-olds in Westminster, Kensington and Chelsea, Wandsworth and Norfolk have been given pounds 1,100 vouchers which can be exchanged for a place at a private school, a state school, or at a playgroup.
The scheme, one of the Prime Minister's favoured projects, is due to be introduced nationally in April 1997. But it now looks likely to cause embarrassment to the Government as Conservative local authorities fight back with aggressive publicity campaigns aimed at keeping children in the state sector.
Wandsworth has spent pounds 3,000 on advertising its services.
Instead of giving extra muscle to the private sector the scheme looks likely to weaken the sector's position, with parents being forced to move their children into state schools to secure their places.
The voucher scheme was designed to lead to the setting up of new private nurseries, but most of the expansion will probably be in primary school reception classes. In Norfolk the Government has paid for 16 local authority nursery units.
Yesterday the Department for Education and Employment said it was too early to say whether any new private nurseries had been opened as a result of the scheme.
Experts say that a reception class is no substitute for nursery education, which must have a qualified teacher for every 13 pupils while there is no limit on primary classes.
Susan Hay, owner of a string of private nursery schools and chair of the Childcare Association, said that the Government had forced unwelcome competition on to schools.
"We have been pushed into battle as a result of the voucher scheme, and it's a battle that doesn't need to happen," she said.
"As for suggesting that parents have more choice, it's a load of baloney. They are going to opt for a good primary school even if it means forfeiting their child's early years in order to get them a place for later," she said.
State-school heads also criticised the scheme. Michael Garratt, head of St William's primary school in Norwich, and the Norfolk secretary of the National Association of Head Teachers, said his school had always taken children without funding at the beginning of the year in which they were five but others would now do the same.
"There's going to be a financial advantage for all schools to take children in the year in which they are five," Mr Garratt said.
A spokesman for the Department for Education and Employment said vouchers gave parents more choice.
"Ministers expect that there will be expansion over time in the state, private and voluntary sectors," he said. "State schools have nothing to fear. There is no need for blackmail."