Heads have warned against reported government plans for bringing in “rigorous mocks” as a back-up in case next year’s GCSEs and A levels can’t go ahead.

The comments came as the debate about whether to hold next year’s exams intensified today.

This morning, a senior Conservative MP suggested that some GCSE and A-level exams could be dropped next summer. But a high-powered group of academy chiefs and educationalists have signed a letter saying that “all exams must take place in 2021”.

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Government plans to hold rigorous mock exams this winter with strict invigilation, marking and grading, and papers produced by exam boards have been reported in The Guardian.

The paper says that education secretary Gavin Williamson is expected to next week announce a three-week delay in the start of next summer’s A levels and possibly GCSEs, alongside the requirement for schools to hold mocks in controlled conditions.

They could be used for final grades where students are unable to sit final exams or their preparation has been disrupted.

However, critics have warned that the high-stakes mocks would lead to students revising early at the expense of learning the rest of the syllabus. One head described the plan as “half baked”.

Vicky Bingham, head of South Hampstead High School, said on Twitter: “On the one hand, the DfE is saying they will push the exam period back in the summer to create more teaching time. On the other hand, by formalising mocks like this they have pushed the exams forward!”

Meanwhile, Robert Halfon, chair of the Commons Education Select Committee, said pupils could be allocated GCSE and A-level grades next year through a “mixed” option in which they are only examined in core subjects while receiving centre-assessed grades in other subjects.

Speaking on BBC Breakfast, the Conservative MP said: “Possibly you could have a mixed version doing the core subjects for exams and maybe assessment for everything else.”

But a letter signed by senior educationalists and published in today’s Sunday Telegraph urges the government not to follow the Scottish government’s example of cancelling exams in favour of teacher assessment.

It states: “Teachers have done a brilliant job during the pandemic, but their assessments cannot be moderated or standardised accurately. We need to let them do what they do best: teach. What’s more, teacher assessment disproportionately handicaps the most disadvantaged pupils.

“We are dismayed by the Scottish government’s decision to cancel National 5 exams next summer. We urge the government to ensure that England’s pupils are not similarly let down. This means that all exams must take place in 2021.

“In the event of difficulties, moves must be made to support pupils. This will require flexibility around timings, and allowances for pupils who are unwell or self-isolating. Exam boards should also be open to giving pupils more choice over which questions they answer, so they do not need to study as much content as they would normally.”

The letter is signed by academy chiefs including Dame Sally Coates, Dame Rachel de Souza and Hamid Patel, alongside other senior figures including Teach First chief executive Russell Hobby and Ofqual adviser and ex Harrow head Barnaby Lenon.

Another academy leader backed calls for exams to run next year but said there also needed to be extra financial support for schools serving disadvantaged pupils.

Stuart Burns, chief executive of the David Ross Education Trust, said: “Exams in 2021 should definitely run, but take place later than usual to give more time for teaching.

“They should be trimmed and simplified (many children sit over 30 papers in the summer), without losing the appropriate level of challenge in the papers. There must be further financial support for schools, targeted for the disadvantaged.

“We also need robust, thought-through contingencies and adjustments in place for our young people, particularly those in deprived areas who all the evidence shows have suffered most from breaks in schooling and worsening circumstances at home.”

The calls backing exams come after another prominent academy chain leader last week called on government to scrap the “gamble” of risky exams in 2021, and research suggested that parents would prefer teacher assessment to be used for final grades.