Nick Clegg has insisted his plans for free school meals for infant school pupils in England will be a "crowning achievement" despite reports of serious official concerns about the scheme within Whitehall.
The scheme has been given a "red" rating in an official risk assessment, indicating that there was a danger of the policy failing, according to the BBC's The World at One.
The Deputy Prime Minister acknowledged that not all schools were ready to implement the policy but asserted they would be by the start of the new term in September.
Prime Minister David Cameron has been forced to intervene in the damaging row between Tory and Liberal Democrat ministers over the coalition's education policy, with the free school meals issue one of the battlegrounds between allies of Michael Gove and Mr Clegg.
Mr Clegg told The World at One: "This is a policy I think is going to make a dramatic difference. I'm incredibly positive about it, I think people are going to look back on this and see it as a real crowning achievement of this Government."
He added: "Already the vast majority of schools across the school system are telling us that they are ready to do it."
Responding to the "red" rating he said: "It is quite normal in Whitehall for people to constantly review the state of readiness of a policy. But let's be really clear, it is mid-May, this is going to happen in September.
"It will happen in September, it is fully funded, we have even gone further than that, we have legislated for it to make sure it is really there to stay."
A Department for Education spokeswoman would not comment on the leaked risk assessment but added:
"The overwhelming majority of schools are already on track to deliver this policy in September and we are
confident the policy will be delivered on time and on budget.
"Universal free school meals have already been shown to work in the pilot schemes run by the Department for Education and Department of Health in 2009. Indeed, schools have had longer to prepare for the introduction of universal free school meals this September than schools in those pilot areas had in 2009.
"Schools are receiving a huge amount of support to provide free school meals. We are providing £150 million to improve kitchens and dining facilities, as well as an additional £22.5 million specifically to help smaller schools to provide these meals."