Pupils isolating because of Covid-19 could miss "high-stakes" mock exams for their GCSEs and A-levels at the start of term, a headteachers’ leader has said.

Former Suffolk head Geoff Barton, who is now general secretary of the ASCL headteachers’ union, said schools would need to think about when to run mocks if they could not take place next week.

He added that schools would also be considering whether to change attendance patterns if they did not have enough staff to cover classes in the new year, although he stressed this would be at the "bottom of the list" of heads' contingency planning.

"The question is whether Christmas has worked as a kind of circuit-breaker or whether you very quickly get increased numbers of staff being affected. There's just lots of uncertainties,” he said.

In November, exams regulator Ofqual published guidance advising that A-level and GCSE students should sit termly assessments to ensure there was enough evidence to determine their grades in case exams were cancelled again.

“Of course, [mocks] have been made more high-stakes this year because we know that as a kind of safety net they may end up counting in the instance that some young people can’t do their exams in the summer," he said.

"So, it's not a case of saying 'let's not bother with mocks', because you will need to do those mocks at some point."