Almost half of Tuesday’s A-level results are expected to be at A* or A in a second year of rampant grade inflation.

It is being widely reported that about 19 per cent of the qualifications are likely to be graded A* this year and a further 30 per cent are expected to be given A grades. The results come after last year’s exams fiasco when 38.6 per cent of A-levels were graded A or A*, up from 25.5 per cent in 2019.

Pupils will achieve roughly a grade higher, on average, than they would have in 2019, the last year that exams were taken, a source said. Grade inflation has also been seen in GCSEs, the results of which are being awarded on Thursday, but not by as much as A-levels, the source added.

The gap between disadvantaged pupils and their classmates is thought to have remained stable. Private school grades are believed to have come under greater scrutiny from exam boards and the regulator, Ofqual, but experts say that the gap between state and private will probably grow.

Exams were scrapped in January after school closures because of the pandemic and replaced with teacher-assessed grades, moderated by Ofqual. Last year an algorithm was initially used to control results but abandoned after an outcry over downgrading and inconsistencies. This year teachers from all schools and colleges had to provide some supporting evidence.

Sir Jon Coles, head of United Learning, one of the biggest academy chains, and a former Ofqual adviser, said he believed 45 to 50 per cent of A-levels could be awarded the top grades. Another education source corroborated this figure.

Coles, a former director-general at the Department for Education, said: “I have not heard of widespread challenge by exam boards to schools’ results.

“All through this there has been the question of whether there could be a meaningful process of ensuring consistency. Frankly, I don’t think there has been. Schools have done their best with the guidance they have had, but they haven’t had the information or process they’d need to be fully consistent.”

Barnaby Lenon, the former head of Harrow who chairs the Independent Schools Council and advises Ofqual, said he was expecting grade inflation and for teachers to err on the side of optimism with borderline pupils.

He said the success of many private and high-performing state schools would be deserved. “They had online teaching from the beginning of the pandemic and a lot of that was live on screens and was effective. I don’t think it’s got anything to do with pushy parents,” he said. “Neither do I think they’ve been inclined to grade more generously than they should have done. If they’ve done well it’s because the teaching wasn’t disrupted to the same degree and the impact of Covid was greater in disadvantaged areas.”

Professor Lee Elliot Major, a leading expert on social mobility, said: “I think there are some really genuine concerns that social mobility will go backwards this year. The gaps in achievement have widened during the significant learning loss of the last 18 months, which we know from research has disproportionately affected poorer pupils.

“There will probably be lots of appeals and it will be those parents with resources and time who will benefit most. We’re inevitably going to see an incredibly big variation between schools when it comes to grades and appeals. It’s likely there will be a widening between more privileged schools [state and private] and others, because the whole system is less regulated.”

Robert Halfon, chairman of the education select committee, said: “There’s likely to be grade inflation. The government has got to make sure the appeals system is fair and easy to engage in and not just accessible to those with barristers for parents.”

Professor Jake Anders, of UCL’s Institute of Education, said that unconscious bias was inevitable in teacher assessed grades: “It’s a very hard thing to be completely neutral about your own students’ work, no matter what teachers are trained to do. In private schools there was both pressure on teachers and better learning — they could react quickly during lockdown because they had the resources and had fewer children with challenges.”

Michelle Donelan, the universities minister, said in a letter to students that an appeals system was in place as a “safety net”. She also said that any school-leaver could repeat the last year of school, “but with such a high rate of projected acceptances [80 per cent of students on to first-choice university courses], we do not think many students will need this option.”