Education Secretary Gavin Williamson has said he will lift the cap on university places in order to help students who may have lost out on their first choice.
Thousands of pupils were told they did not get the grades to attend their top choice uni after results were downgraded using an algorithm.
But a screeching u-turn from the government means those pupils will now be awarded their predicted grades.
Some however may have already lost out on a place, with it going to another pupil via clearing.
Mr Williamson has said that universities will not be fined for going above previous limits to help accommodate students affected by the exam grading decision.
Alistair Jarvis, chief executive of Universities UK, said: “Today’s policy change will mean that more students will have the grades that match the offer of their first choice university. This will cause challenges at this late stage in the admissions process – capacity, staffing, placements and facilities – particularly with the social distance measures in place.
“We are seeking urgent clarification and advice from Government on a number of crucial issues.
“Almost 70% of students are already placed with their first-choice institution, but those who are not should think carefully about their next steps, speak to their parents, guardians and teachers and get into contact with their preferred university to advise on their options.”
John Craven, Chief Executive of upReach, said: “It is not yet clear that all will be able to honour their offers given capacity constraints – even if the student numbers cap at each university is indeed lifted.”
Paul Whiteman, general secretary of school leaders’ union NAHT, said: “It may already be too late for some A-level students who have already missed out on their first choice of university and course.
“Every day of delay is going to have loaded more and more difficulty onto universities and their capacity to meet all of the demand for places that will now inevitably come their way. For them, the problem is far from over.”
David Hughes, Chief Executive of the Association of Colleges, said: “It is vital that information is provided speedily on how this decision will impact on higher education institutions, students wishing to apply through clearing and those who may have been rejected on their original grades.”
Laura Rettie of education consultancy Studee said: “Universities are going to be thrown into disarray. I just hope that universities will have the capacity to deal with this change and can accommodate students who should have been given places.”
David Laws, Executive Chairman of the Education Policy Institute (EPI), said: “Universities must now offer maximum flexibility for those A level students who had missed out on a place under the previous grading system.
“Those students who were originally offered a place under teacher assessed grades should now have their place reinstated or deferred to next year.”
Admissions body UCAS said pupils should take some time before rushing into a decsion.
In advice to pupuls they said: “For those students who were not placed with their firm (or insurance) choice university, our advice is that you don’t need to make your decision immediately.
“Speak with your parents, guardians and teachers and then your first conversation will need to be to your firm (or insurance) choice university.
“Once your university has your ‘Centre Assessed Grades (CAG)’ via exam bodies they can make a decision as to whether there is a place at your preferred choice.”