The Government's promise of a free nursery place for every four-year-old in England will push many into overcrowded school reception classes, say early-years campaigners.
Last week Labour unveiled its early-years development plans, outlining how its pre-election nursery pledge will be met.
But voluntary and private nursery providers claim they are still under threat as many of the country's 650,000 four-year-olds will be "hoovered up" by primary schools.
Liz Murphy, of the National Campaign for Nursery Education, said she was "very worried". "Four-year-olds need education based on play and we don't believe that will happen in large reception classes," she said.
Four out of five of the extra 60,000 places created by Labour will be in state schools and the rest in private or voluntary nurseries, for which the Government will pay pound;1,100 per child per year.
Launching the plans Estelle Morris, the education junior minister, would not say how many four-year-olds would join five-year-olds in reception classes.
Mike Hipkins, of the Department for Education and Employment under-fives division, said the plans heralded a new phase of partnership and co-operation and would put an end to "recent wholesale closures of playgroups and nurseries".
However, Margaret Lochrie, of the Pre-school Learning Alliance, claimed that despite ministers' genuine goodwill and sincerity she didn't expect the 1,500 playgroups currently facing closure to be saved.
She said: "You don't get partnership just by saying the word. Many of our groups were given five minutes' notice of the local authority plans, before they were expected to contribute. With almost all the four-year-olds in the state sector and pre-schools still in jeopardy, provision for three-year-olds is in serious danger."
Rosemary Murphy, of the Private Day Nurseries Association, said many private nurseries had been fearful of criticising authority plans. She said: "Many nurseries were deeply unhappy with the partnership proposals authorities put forward. But if they'd voted with their feet by not taking part, they could have been left out altogether. There are some very nervous nurseries waiting to see if they've signed their own death warrants."
Pre-schools and private nurseries want a national steering committee, made up of all three sectors, to monitor the implementation of the plans in September.
Teaching unions welcomed the plans. Nigel de Gruchy, general secretary of the NASUWT, said: "We've campaigned for years for an expansion of nursery schooling. We have no doubt that genuine education opportunity for young children pays great dividends in later years." However, he too warned that the DFEE would need to make sure that reception classes did not mushroom.
Higher numbers of young children in reception classes are likely to increase calls to introduce a more flexible, play-based curriculum for under-sixes as reported in last week's TES. Ms Morris said authorities must "demonstrate how the special needs of four-year-olds are being met".
Only two local authorities - Oxford and Bournemouth - had their plans refused for failing to develop good enough partnerships.