Council chiefs have once again cast doubt on plans by Oldfield School to open as an all-girls academy this autumn.

Head teacher Kim Sparling is confident that the Department for Education (DfE) will approve her plans in time for her to open as an academy before Christmas.

But Bath and North East Somerset Council has issued an ultimatum to the school asking it to change its proposal so it would become co-educational – or risk being shut down.

The authority's divisional director for children's services, Tony Parker, said he believed it was "very unlikely" that Oldfield would be allowed to remain as an all-girls school.

The school's outstanding Ofsted rating means it could potentially be fast-tracked for academy status by Education Secretary Michael Gove – but the minister's officials have been bombarded by letters from people in Bath calling for him to insist that boys be let in.

Mr Parker said: "Oldfield School is subject to a local authority reorganisation proposal and that means the DfE will not approve it to become an academy straightaway.

"It is very important that people understand that the council is in favour of academies, but in this case the school remaining all-girls is not what the community wants and is not what is right for education in Bath.

"I think it is very unlikely that the school will reopen as an all-girls academy."

In the school's July newsletter, Mrs Sparling said she remained confident that the DfE would approve the academy plans, with the change of status happening during the autumn term.

She wrote: "Recently a civil servant from the DfE came to discuss our conversion plans.

"It was a very positive meeting; I was pleased to have the opportunity to discuss what we see as the benefits of having more control over this school's destiny outside of local authority control.

"I'm aware that the local authority had been saying to the local press they will veto our plans to become an academy.

"The DfE official confirmed that the LA do not actually have the right of veto."

The school has told the Chronicle that B&NES Council had not offered it any money to become co-educational, something the authority – which says it is happy to pay for new toilets, changing rooms and an all-weather sports pitch – strongly disputes.

Mr Parker said that an offer of around £1 million for Oldfield School to carry out the necessary changes to start admitting boys had been on the table for a number of years.

B&NES has given Oldfield's governing body until September 17 to change its academy application so it will become co-educational.

If it does not, the authority will consult on closing the school.

It would then plan to reopen a new co-educational school on the same site, which would probably not be under local authority control.