Figures published by the Department for Education based on a survey of providers show that 44,250 early years providers are planning to offer 30 hours, compared with 54,900 providers that currently deliver the 15-hour offer. This works out as 10,650 fewer, or 19 per cent.
The DfE data shows that there are currently 22,700 pre-schools and nurseries offering 15 hours of free entitlement. But only 14,600 pre-schools and nurseries say they definitely plan to offer the 30 hours.
Meanwhile 8,200 primary schools with nurseries currently offer the 15 hours, but only 3,900 say they intend to offer 30 hours.
In addition, 350 maintained nursery schools plan to offer the 30 hours, compared with 400 that currently offer the 15 hours.
The only provider type likely to see an increase is childminders, with 25,400 planning to offer the 30 hours, compared with 23,600 who currently offer the 15 hours.
The DfE said that the survey was conducted between March and July 2016, before full funding details for 30-hour provision had been finalised.
But Neil Leitch, chief executive of the Pre-school Learning Alliance, said the statistics support what his organisation has been saying for some time - that without adequate funding, many early years providers will be unwilling to deliver the 30-hour offer.
"What's most alarming is that these figures were gathered at a time when many providers thought they would be receiving close to the average funding rate of £4.88 per hour," he said.
"With final rates currently being confirmed across the country, and many providers discovering that they'll be receiving significantly less, we would expect the number of settings opting out of the 30-hour offer to be even higher than these statistics suggest.
"Even more concerning is the fact that government has confirmed these funding rates will be frozen until 2020, despite significant likely increases in childcare business costs such as wages, rents, mortgages and business rates.
"This means that even those childcare providers who can somehow make the offer work this year are likely to struggle in the years to come, and so we are likely to see the number opting out of the scheme increasing over time."
A DfE spokesman said: "It's great to see that the majority of providers intend to offer 30 hours childcare, backed up by our record investment of £6bn per year in childcare by 2020.
"Since this survey was conducted, we have published our Early Years National Funding Formula, which will see increased hourly funding rates for the vast majority of providers and our early implementers are now successfully delivering the offer a year early.
"Alongside our record investment, we are creating a workforce strategy to help attract, retain and develop the very best staff so that we deliver childcare that is both affordable and high quality to families across the country."
The 30-hour childcare entitlement is to be introduced from September.