The exam regulator Ofqual has said it will advise the government on whether its timetable to scrap GCSE for E Bacc is workable.
Edcuation Secretary Michael Gove told the Commons that GCSEs are to be replaced by a new English Baccalaureate Certificate in secondary schools in England, the biggest change in exams since the 1980s.
The first EBacc courses in English, maths and sciences will begin in September 2015 and children will sit exams in these subjects in 2017.
Chief Regulator Glenys Stacey said that Ofqual would continue to put standards first and would advise on the timeline for change to ensure that the proposed new qualifications can be implemented safely.
In a letter to the Department for Education, she said:
"We will advise government on the timetable for change, and say if it is not achievable or if the risks to standards or delivery are unacceptable.
"We will wish to identify the delivery pressure points in the reform of GCSEs and intervene if we need to in order to manage any unacceptable risks.
"Our role will be to ensure the safe delivery of all qualifications – both new ones and existing ones – during and beyond the period of reform.”
Mr Gove also announced only one exam board will set the exams for each subject.
"Safe delivery will depend to a large extent on the decisions on qualifications that government makes, and the effect then on each exam board," Ms Stacey said.
"There are longer term considerations as well, and we will begin work now on how they might be managed."
Mr Gove told MPs:
"After years of drift, decline and dumbing down, at last we are reforming our examination system to compete with the world's best."