Applicants to Oxford University who successfully appeal over their A-level results have been told they may have to wait a year before they can start their degree courses.

Some students who achieve the top grades after challenging their results could have their places at Oxford deferred until autumn 2021 if the institution reaches maximum capacity.

The university has said it would not be possible to meet “ongoing social-distancing restrictions” and other challenges presented by Covid-19 if it went above its maximum intake of students.

Cambridge University has also said students may be asked to defer their entry until autumn 2021 – depending on when they find out their appeal outcome.

The move comes after Universities Minister Michelle Donelan told universities to hold places for applicants challenging A-level grades until they receive the outcome of their appeal.

On the suggestion that some applicants could be asked to defer places until 2021 if they appeal, shadow health minister Justin Madders tweeted: “Haven’t these kids gone through enough already?”

The Ucas deadline for applicants to meet their academic offer conditions is September 7, which leaves exam boards less than four weeks to issue outcomes of appeals.

The Government announced late on Tuesday that A-level and GCSE students will be able to use results in valid mock exams to appeal if they are unhappy with their results.

But schools, colleges and universities are still unclear how the new appeals process will work and what the likely timescale will be.

England’s exams regulator, Ofqual, has said it is “working urgently” to set out how mock exam results will form the basis of an appeal, but further details will not be ready until next week.

On A-level results day on Thursday, Ofqual revealed that 39.1% of teachers’ estimates for pupils in England were adjusted down by one grade or more.

Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: “We would encourage universities to show some flexibility about applications, and not to undermine the appeals process by insisting students must defer.

“These are unique circumstances in which students who were on course for places and have not had an opportunity to sit exams are at risk of losing out because of a statistical algorithm used to calculate their grades. They deserve a spirit of generosity.”

A University of Oxford spokesman said: “We intend to take every student who meets their offer grades as well as those where we consider there are mitigating circumstances for them missing their grade.

“As we do every year when grades are re-marked, some students may be offered a deferred place.

“Once we reach our maximum intake of undergraduates in 2020, we will have to defer entry to 2021 for any additional candidates who appeal successfully and whose place is then confirmed.”

He added: “Our primary concern must be the health and safety of our students, staff and community and it will not otherwise be possible for us to meet ongoing social-distancing restrictions and other challenges presented by the Covid-19 pandemic.”

Hillary Gyebi-Ababio, vice-president of higher education at the National Union of Students, said: “Too many young people have lost out on life-changing opportunities or are being told they will have to put their lives on hold in the hope of securing places at the universities of their choice.

“The Government’s failure to ensure an adequate and timely appeals process was in place before A-level results day was wholly avoidable, and they must now act to address this crisis.”