A community secondary is looking to convert to faith-school status after it becomes an academy, a move which is the first of its kind and has sparked fears it will be followed by many others.
Malton School in North Yorkshire has written to parents explaining that it intends to become an academy, then apply for a change in its religious character to return to the Church of England.
In a letter sent last month, headteacher Rob Williams said the school wants to consult on re-establishing itself as Malton Grammar School. Under the proposals, it will remain unselective and return to the Church, which it left 100 years ago.
If the plans are agreed, the school would become "Malton Grammar School - a Church of England Academy".
Mr Williams said: "We believe that a reconnection with the Church family of schools offers the best prospect of a genuine network that will sustain and strengthen us in the years to come.
"Malton School still retains strong elements of its ethos that can be traced back to its history as a church foundation from 1547 to 1911. In discussion with senior education officers from the Church, we feel that our existing aims and ethos match up closely and that a formal link will add value to our work."
But the move has been greeted with concern by the British Humanist Association, a non-religious campaigning organisation, which believes it will open the door to a wholesale return of schools to the Church.
Richy Thompson, a campaign officer at the association, said while it was difficult to estimate how many schools would attempt the switch, it has become a "much more serious issue" since the Coalition expanded the academies programme.
"We have been saying all along it appears to be easier for academies or free schools to convert to having a religious character. We believe Malton School feels the same way. That is why the school is converting to be an academy first," Mr Thompson said.
"We are very concerned. It is something we have been working on for a good while. It is clear this school would not be doing this if not for the fact they can do it without the local authority. We know the school believes the local authority would not approve the change."
But a spokesperson for the CofE said the two processes in converting to academy status and changing a school's religious character were "quite separate".
"The ministry lays down very detailed consultation separately on the two issues," the spokesperson said. "As far as community schools becoming Church schools (is concerned), it is not something that happens every day.
"At the most, we only see around half a dozen schools or so that go through that process a year, so there is no necessary connection between it and conversion to academy status anyway. However, we would emphasise that our schools are for the whole community."
In a statement, North Yorkshire County Council said it will be asking for evidence about why the change is needed and whether it will have the potential to restrict access for certain children.
It said: "Becoming a faith-based school is quite different in school organisation terms from becoming an academy and should be approached quite differently.
"Issues around admissions and choice are particularly sensitive when a school is the only one serving a large rural area."