Private schools are likely to continue offering A-levels under the Government’s planned shake-up of post-16 education, England’s exams regulator has said.

The Prime Minister announced plans last year to introduce a baccalaureate-style qualification in England – the Advanced British Standard (ABS) – which will eventually replace A-levels and T-levels.

In its response to a consultation on the new qualification, Ofqual said the scale of change needed to achieve the ambitions of the ABS is “unprecedented” and would require “significant investment”.

The regulator added that “unregulated” A-levels could be taken in private schools even if A-levels are no longer available in state schools in England.

“This could present a confidence or reputational challenge for the ABS,” Ofqual warned.

Parents, teachers, students, employers and education leaders were invited to share their views on the ABS in a consultation which closed in March.

It came after Rishi Sunak announced that 16 to 19-year-olds in England will typically study five subjects rather than three, and they will choose a combination of subjects at both “major” and “minor” level.

In its response to the consultation, Ofqual said: “Achieving the ambitions of the ABS requires change on a scale unprecedented in England in recent decades.”

It added: “Reform on this scale can be delivered successfully, but its scale and complexity require significant investment of resource across all parts of the education system.”

In October, Mr Sunak said the ABS would bring together A-levels and T-levels – the Government’s flagship technical qualification – into a single qualification.

All pupils would study some form of English and mathematics until the age of 18, he said.

Once fully rolled out, the ABS would replace A-levels and T-levels, No 10 said.

In its consultation response, Ofqual said the A-level brand has “accumulated public recognition and confidence at home and internationally”.

It added: “Given the high level of recognition that A-levels have accumulated, it is likely that awarding organisations will continue to offer unregulated ‘international’ A-levels, even if the ABS means that A-levels cease to be regulated qualifications available in state schools.

“These A-levels could be taken in UK independent schools and abroad.”

The exams regulator called on the Department for Education (DfE) to consider “a staged approach” to the reforms, with mandatory maths and English introduced first with a focus on investment on the teacher workforce.

Barnaby Lenon, chairman of the Independent Schools Council (ISC), said: “Independent schools will have differing views of the Advanced British Standard.

“But I would say it is likely that some will move to an international A-level option as Ofqual suggests, especially if international A-levels are regarded as being of a higher academic level than the ABS and universities in the UK welcome them.”

Tom Middlehurst, curriculum, assessment and inspection specialist at the Association of School and College Leaders (ASCL), said: “The approach the Government has taken with the Advanced British Standard is fundamentally flawed.

“As Ofqual has pointed out, introducing a new system of qualifications is deeply complicated and not something that can be done on the fly.

“The starting point should have been for consultation on the underlying principles of what we want students to study at the age of 16-19, followed by detailed consideration of the most appropriate qualification and assessment structures.

“By announcing the Advanced British Standard almost out of the blue, the Government has left the education sector with more questions than answers.”