Dozens of middle schools have expressed interest in becoming academies as local school reorganisation plans put their futures at risk.
More than 40 middle schools have approached the Government about converting to academy status, which local authorities fear could throw into disarray plans to reorganise schools and cut surplus places.
At least 20 of the schools interested in making the switch are rated "outstanding" by Ofsted, meaning they are pre-approved to become academies under the Government's criteria.
Campaigners have seized on the expansion of the academies programme and the planned introduction next year of free schools as a way to protect the future of middle schools.
Nigel Wyatt, executive officer of the National Middle Schools Forum, said: "One of the main reasons for getting rid of middle schools is to remove surplus places.
"In future this might not be an option for local authorities. They will find planning in this way much more difficult, so it might be good news for middle schools."
The interest from middle schools comes as the Government announced this week the first wave of schools that will convert to academy status this term. Just 32 schools will be ready to convert to academy status at the beginning of this term, considerably lower than ministers had first hoped for. At least 140 are expected to convert before the end of the year.
Middle schools interested in academy status come from across the country, including Dorset, Somerset, Suffolk and Worcestershire. Schools that have gone through with full applications to convert include a federation of three middle schools from Bedfordshire and another from Northumberland.
However, local authorities have warned that middle schools applying for academy status could wreck years of planning devoted to reorganising school places.
Graham Newman, the councillor responsible for children's services at Suffolk County Council, said his authority was halfway through the process of transforming from a three-tier system - with first, middle and upper schools - to a two-tier system of primaries and secondaries.
"We will be in dire trouble if we do not get this done; ministers need to explicitly understand that," he said. "We must be able to finish this job and I have written to ministers to explain that."
The warning comes after the axing of the Building Schools for the Future programme, which also disrupted local authorities' reorganisation plans.
The Department for Education has said it checks to see if a school is "in a secure position" to become an academy.
Significant changes since its last Ofsted rating, a budget deficit, or being part of school reorganisation plans can stop schools winning approval.
A DfE spokesman said: "We deal with each application on a case-by-case basis. The Secretary of State expects to approve all outstanding schools applying, but we have set out clear exceptional circumstances which may prevent this - including wider local school reorganisations.
"We will work closely with individual schools and local authorities to assess the specific, individual circumstances before making a decision."
Endangered schools grab at academy lifeline, pages 28-29.