Plans to allow childminders and nursery staff to look after more children in England are in "chaos", Labour says.It follows Deputy Prime Minister Nick Clegg admitting he had doubts about whether it would cut costs for parents, and also concerns about child safety.
Labour's Stephen Twigg asked an urgent Commons question on plans he said faced "overwhelming opposition".
Education minister Elizabeth Truss told MPs the current system was not working and was unaffordable for many people.
According to leaked letters seen by the BBC's James Landale, Mr Clegg gave Ms Truss the clearance to press ahead with a consultation on the policy in December.
Some Tory sources have asked why Mr Clegg did not raise his concerns about safety and impracticality at the time - but the Lib Dems insist Mr Clegg signed up to a consultation, not a policy.
'Better value' Responding to Labour's urgent Commons question, Ms Truss said the government was now considering responses to the consultation and would make further announcements "in due course".
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She said no nursery or childminder would be forced to look after more children, and the government was giving them the chance to exercise more professional responsibility."The current system of childcare is not working for parents, too many parents in the UK are struggling to juggle their work and childcare arrangements."
Ms Truss said the government spent £5bn on childcare and needed to get "better value for money for the investment the government puts in".
"At present, we have the tightest ratios in Europe for children under three and we also have the lowest staff salaries," she said.
But Nick Clegg has now spoken out to say he doesn't believe that policy will work. He doesn't think any savings will be passed on by the nurseries and believes the policy is unpopular with parents.
What is striking is there appears to be no attempt, particularly by the Conservatives, to play down the difference in the views between the two coalition parties.
So we have Nick Clegg making his views known on his weekly radio phone-in, and then, minutes later, Conservative minister Liz Truss giving a robust defence of the idea in the Commons.
She says the UK has some of highest adult-to-child ratios in Europe and without action, the high charges will stop some people getting back into work.
Grant Shapps, the Tory chairman, insists the reforms to childcare ratios will still happen.
But the divisions between the two party leaders over one of the coalition's flagship policies - David Cameron has said sorting childcare out was the "holy Grail" of UK politics - could now put the policy in jeopardy.
She argued that without reform, "we are going to find that it becomes prohibitive for many parents to afford childcare and be able to go out to work"."These policies are alive and well in France, Ireland, in Holland and in Germany. There is not a single country, including Scotland, where ratios are as low as they are in England."
The plans would allow nursery staff to look after four babies instead of three and six two-year-olds, instead of the current limit of four.
Home-based childminders would be allowed to look after two babies under one, instead of one as currently, and four one-to-five-year-olds, up from three.
But carers' qualifications would have to meet new standards.
The plans were due to be implemented in September but have been met with opposition from some parents' groups and charities.
BBC News Channel chief political correspondent Norman Smith said there appeared to be a rift between Lib Dem Mr Clegg and Conservative Education Minister Elizabeth Truss over the issue and it was difficult to see how the policy could proceed, unless David Cameron threw his weight behind it.
Mr Clegg told LBC similar changes for three- and four-year-olds under the previous Labour government had had "almost no effect" on childcare costs for parents.
He said the government was "grappling" with the issue and had to "get the balance right".
"We've been talking about this for weeks and weeks," he said.
Speaking in the House of Commons, shadow education secretary Stephen Twigg said the split was "another example of chaos and incompetence at the heart of government, particularly in the Department of Education".
He said the scale of opposition to the plans had been "overwhelming" and told the BBC: "Nobody wants this, parents don't want this, the experts don't want this, the government's own adviser on childcare, Cathy Nutbrown, has said this isn't a good idea."
Conservative backbencher Peter Bone told MPs Mr Clegg should make his remarks in the Commons, not on the radio, and the government should "press on and ignore the Liberal Democrats" over the policy.