Ofqual has said that "a number of issues" would need to be resolved before pupils could sit online assessments in 2021, if exams were to be cancelled again in the event of further lockdowns.
Two weeks ago, Ofqual chair Roger Taylor said that online tests could be used as a part of a "plan B" if GCSEs and A levels were cancelled next summer.
Background: Pen and paper must go, says Ofqual head
Answering questions from the Commons' Education Select Committee over the grading fiasco this summer, Mr Taylor said that teacher-assessed grades should not be used if exams were cancelled, but online tests could be.
"In terms of a plan B [for 2021] based on centre-assessed grades, our strong view would be not to do that," he said.
Asked what should happen if exams could not take place next summer, Mr Taylor added: "There are mechanisms, such as additional papers; there are other mechanisms, including, for example, using online tests."
However, when Tes asked Ofqual for further details regarding the online tests, including how they would be moderated if pupils were to sit these at home, potential difficulties for pupils with SEND, and for pupils who lacked online access, the regulator admitted that there were a "number of issues" to work through before these were used.
An Ofqual spokesperson said: “Our focus continues to be on providing sufficient surety about 2021 timetabling for exams, and making sure teachers and schools have all the right information about the subject content to be taught and are familiar with the changes to assessment already announced for some subjects.
“If circumstances mean that traditional examinations are not possible then online assessments may be able to make a contribution to any alternative arrangements.
"However a number of issues would need to be worked through first, including those raised. We anticipate saying more on contingency arrangements in the coming weeks.”
Previously, some commentators have raised concerns about how online exams could be made fair for all pupils.
In 2011, when the idea of online GCSEs and A levels was mooted, Examination Officers' Association chief executive Andrew Harland said there could be issues in making exams accessible for pupils with special educational needs.
And educationalist Dylan Wiliam has previously questioned how pupils would draw graphs for mathematics exams in online tests.
A further question in 2021 is how exams would be monitored to ensure malpractice did not occur if pupils were sitting tests at home.
Geoff Barton, general secretary of the Association of School and College Leaders, said there were "obvious logistical challenges" in implementing the idea.
“We heard the chair of Ofqual in his evidence to the education select committee suggest the idea of online tests as a contingency measure if exams are disrupted by local lockdowns, but we haven’t seen any details about how this might work," he said.
"There are some obvious logistical challenges around how students without online access would carry out these tests, and how it would be possible to ensure a level playing field.
"These may well be solvable, but it seems like a major undertaking and there isn’t much time to turn it around.
"Ofqual and the government cannot afford to bank on an untried system which doesn’t yet exist as a contingency plan.
"The danger is that it may be difficult to deliver and we will be left with nothing. They have to put in place a solid back-up plan now. The obvious thing is to have some form of assessment in the autumn and spring terms upon which grades could be based if students are unable to sit exams. But we are running out of time and this needs to be sorted out urgently.”