More than 2,700 schools - around one in three assessed so far - will have to improve their kitchen facilities if they are to provide free meals for infant school children, figures revealed.
Some require a complete refurbishment, while others need little more than a dishwasher or microwave to give all infant school pupils a free meal from September, a policy announced by the Liberal Democrats last year.
The figures, obtained by the BBC using Freedom of Information laws, found that more than 1,700 schools had no kitchen at all, meaning they will have to have hot meals cooked at nearby schools and brought in or provided by external caterers.
Of the 152 local authorities that provided information, some said their funding allocation was sufficient to carry out the improvements, while others said they would need more.
The Government is providing £150 million to upgrade school kitchens, which Lib Dem sources last month said was expected to be enough to provide the necessary facilities.
Deputy Prime Minister Nick Clegg also said that while the free school meals would have to be healthy, rules would not be imposed on whether they always have to be hot, giving rise to claims children will be handed packed lunches.
A Department for Education spokesman told the BBC that free school lunches for all infant children would save parents money, improve pupils' education and ensure more children eat a healthy and nutritious meal at least once a day.
"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," the spokesman said.
"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 £150m to improve kitchens and dining facilities, as well as an additional £22.5m specifically to help smaller schools to provide these meals."
Schools Minister David Laws said he was "not complacent" about the problems but insisted that most schools were on track to deliver the service.
He told the BBC Radio 4 Today programme: "The anecdotal evidence and the noise that you tend to get will tend to be from what can sometimes be a small minority of schools, and I take their concerns seriously.
"What you don't hear about, and what I do hear about, is the vast majority of schools that are on track to deliver this."