The inspectorate has revealed that between the end of March and end of August this year there were 752 fewer registered childminders.
This is a fall of two per cent over the five month period and brings the total number of childminders to have left the profession since the end of August 2012 to 14,669, a fall of 26 per cent.
At the end of August this year childminders offered 20 per cent of all childcare places, amounting to 253,900 places, which is two percentage points down on August 2012's figures.
Pre-school Learning Alliance chief executive Neil Leitch said he is concerned about the continued exodus of childminders from the early years sector, especially as more places are needed to deliver the 30 hours per week free childcare offer for three- and four-year-olds.
"It is incredibly concerning that the number of childminders in the sector is continuing to fall at such a rapid rate," said Leitch.
"To lose nearly 15,000 childminders over the course of five years is clearly a completely unsustainable position and it's time the government took action to tackle this decline.
"Childminders are a vital source of quality, flexible care and education, and will be vital to the long-term delivery of the 30-hour scheme. With some areas of the country already struggling to meet the demand for 30-hour places, now more than ever, we cannot afford to be losing experienced, quality practitioners from the early years workforce."
Leitch added that a key factor in the decline in childminder numbers is a lack of parity with the rest of the early years sector, with government too often seeing them as an inferior option to nurseries.
"In addition to years of inadequate funding, childminders have suffered from a real lack of parity with the rest of the early years sector for many years," said Leitch.
"With the government continuing to promote them as a way of covering the awkward hours of provision that nurseries and pre-schools may not offer, rather than quality, professional providers in their own right, is it any wonder that many are choosing to look for a career elsewhere?"
Liz Bayram, chief executive of the Professional Association for Childcare and Early Years, also said she was "deeply concerned" by the latest figures.
"Childminders need more help with start-up costs and a removal of the key barriers preventing them from delivering funded places," she said.
"This means a higher hourly rate; an end to delayed payments and burdensome red tape from local authorities; and a removal on the ban on childminders providing funded places to related children.
"These are all factors contributing to a decline in childminder morale and sustainability that government could resolve."
Meanwhile, Ofsted figures obtained by Labour's shadow early years minister Tracy Brabin show there has been a net loss of 1,146 nurseries and childminders from the early years register since 2015. Of those that left, 81 per cent were rated either good or outstanding.