Action is needed to prevent people with "extremist religious or political" views taking over academies, a board member of the country's largest sponsor has warned.
Geoffrey Davies, on the board of the United Learning Trust (ULT), which sponsors 17 academies, called for new rules that would stop an academy trust passing to groups "alien" to a school's original ethos.
The news comes as schools minister Lord Hill said in a letter to the National Secular Society (NSS) that the Government will not legislate against proselytising in schools as more academies and free schools are established.
Speaking at a Westminster Forum earlier this month, Mr Davies said it was currently too easy for an academy trust to fall into the wrong hands and that the Government has very little power over it.
"There has got to be some provision that is built into the documentation for the transition from one group of people running (an academy trust) to another," he said. "There is nothing at the moment that controls who those people are.
"Those of us who played student politics back in the 1960s know how easy it is to take control of organisations and it would be very easy for an academy trust to become controlled by a group of people who are completely alien to the original concept.
"People with extremist religious or political views could work their way into control over a period of time and at the moment there is nothing that the department can do to affect that, except to give a seven-year notice to terminate the agreement."
The issue is a chief concern of secular groups, particularly the NSS, which wrote to Lord Hill raising fears that extremist religious groups could take control of schools and "brainwash" their pupils.
With the growth of academies - and the introduction of free schools - increasing numbers of schools will be given freedom to operate outside the normal constraints of the national curriculum.
However, Lord Hill said in a letter to the NSS that he "did not think it appropriate" to legislate, as parents will choose a school based on its ethos.
Lord Hill wrote: "That ethos may be Christian, Muslim or Jewish or it may have no faith ethos at all. Parents should be free to choose schools on the basis of their ethos. I would like to believe that parents consider these issues carefully and send their children to a school fully aware of its faith or other ethos."
Terry Sanderson, president of the NSS, said: "We are alarmed at the prospect of extremist religious groups taking control of these schools and using them to brainwash children. What is to stop a Muslim group taking over a school and turning it into a madrassa at public expense if that is what parents want?
"What is to stop a Scientology front group taking over a school and then introducing its teachings with taxpayers' money? The fact that some parents want to indoctrinate their children in a particular religion does not mean that they should be able to access public money to do it."
A Department for Education spokesman said there was "no question" of this happening.
"We will not allow any extremist group to set up an academy and in the highly unlikely event that an existing academy strays from what is acceptable, we have powers to stop their funding and even take over the governing body," he said.
"The academies programme has never been and never will be about fringe beliefs and view points - it's about high-quality education."