Less than a decade ago it was unheard of for an independent school to transfer to the state sector.
But new Department for Education figures shared with TES reveal that 27 former independent schools have become state-funded since 2007, with nearly half of them switching in the past two years (see panel, below left).
Hans van Mourik Broekman, the principal of Liverpool College - a prestigious independent school that became a state academy in 2013 - held a conference for new entrants to the state sector last month and is expecting numbers to swell further.
"It has gathered pace, and I think there will be more of it, not less," he told TES.
But the move is not without its risks. Headteachers that TES spoke to this week talked about the prospect of tough inspections from Ofsted and negative reactions from parents.
John Moreland is headmaster of Polam Hall School in Darlington, County Durham, which will become a state-funded free school from September. He said that some parents disagreed with the move - about 10 children were taken out of the independent school as a result of the decision. However, the majority were supportive.
"Some took a pragmatic view," Mr Moreland said. "They told us it was not necessarily what they would have wanted but they understood why we were doing it, and they were pleased they would be saving money."
The announcement of the shift had already broadened the school's socio-economic base, even before the end of fees this coming September, he added.
"Parents knew that if their children started in September 2014 they would only have to pay for a year, and they wouldn't have to reapply to join in 2015," he said.
"We've had people remortgage their homes, sell their cars and sacrifice holidays. These are people who couldn't have afforded an ongoing private education."
In the 1970s, more than 100 former state-funded grammars started charging parents fees as independent schools after their old central government "direct grants" ended.
William Hulme's Grammar in Manchester was among them. But in 2007 the school was at the forefront of a new exodus in the other direction.
Mr Broekman said that many of the schools that had converted or were thinking of doing so were based in the North of England, and were making the move as a result of the recession and the fact that fewer local families could afford fees.
"Demographics are usually a big issue, which is why we're not seeing this phenomenon very much in the South East and London," he said.
"In Merseyside, the number of people who can afford to pay upwards of pound;10,000 [a year] in fees is very small. We didn't want to become a school with a shrinking roll that served only the very wealthy."
Similarly, Mr Moreland said a falling pupil roll prompted his school to make the switch. "The North East has seen a decline in the number of students attending fee-paying schools since the start of the recession," he said. "We started to look at alternatives before we got to the point of no return."
State schools, many of which are facing real-terms cuts this year, might question why others would abandon money from fees and step into the fraught world of government funding.
Simon Corns, headmaster of Queen Elizabeth's Grammar School in Blackburn, Lancashire, which became a free school in September, acknowledged that funding was difficult. "Of course I'm worried but there isn't a headteacher in the country who isn't," he said. "We were not a wealthy school [as an independent] and we'll do our best to offer value for money."
Neil Blundell, principal of Bristol Cathedral Choir School, which became an academy in 2008, agreed. "It's a tough time to be in the state sector, and I think it will be tough for the life of this Parliament.but I don't think anybody [at the school] has regretted the move to the state sector," he said. "Students and staff have been enriched immeasurably."
One major change for the converter schools is the introduction of Ofsted inspections, which differ significantly from the peer reviews carried out by the Independent Schools Inspectorate (ISI).
Mr Broekman said the change could be difficult. "Independent schools are interested in the whole person and have extensive extracurricular provision and activities. Ofsted doesn't put the programmes we're interested in at the centre of their inspection framework," he said.
But Mr Corns said the differences between Ofsted and the ISI were sometimes "exaggerated", and that he had learned a lot from state schools' use of data and the way Ofsted inspected this. "On pupil tracking, the state sector is light years ahead," he said. "State schools are better at identifying very quickly where pupils' needs are and doing something about it."