Reopenings of schools next week may be delayed as part of measures to tackle soaring coronavirus case numbers, scientists advising the Government have suggested.

School leaders have also warned that teachers and pupils may be put at risk if secondaries reopen, as planned, while a new ultra-transmissible strain of Covid-19 is driving a rise in hospital admissions.

Earlier this month, the Government said exam-year students would go back to school as normal after the Christmas holidays, but the majority of secondary school pupils would start the term online to allow headteachers to roll out mass testing of children and staff.

But experts have suggested any reopening may have to be delayed.

It came as Conservative MP Robert Halfon, chairman of the Commons Education Select Committee, said he “hope(d) very much” that schools would reopen from Monday, but called on Prime Minister Boris Johnson to “set out a long-term plan for education” and end confusion about the future of schooling during the pandemic.

He told Good Morning Britain: “I would welcome a statement either from the Prime Minister or the chief medical officer as to what the scientific evidence is, and also to set out a long-term plan for education – a route map out of this – because we can’t have schools as a revolving door, with parents, the teaching profession and support staff not knowing from one day to the next what is going to happen.”

Latest figures from NHS England show there were 20,426 patients in NHS hospitals in England as of 8am on Monday, compared with the 18,974 patients recorded on April 12.

Professor Andrew Hayward, a member of both the Government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) and the Scientific Advisory Group for Emergencies (Sage) suggested that allowing pupils to return to schools would mean stricter restrictions in other areas of society.

He told BBC Radio 4’s Today programme: “We’ve had control measures that were previously controlling the old variant are not enough for this variant.

“And so if we want to control the new variant we are going to need much tighter restrictions.”

What looks like is going to happen is possibly a slight delay to the start of term, and then ramping up mass testing to ensure that we rapidly detect cases

Prof Hayward said he thinks schools will have to return “maybe a little bit later” but that it would mean “we’re going to have to have increased, strict restrictions in other areas of society to pay for that”.

Fellow Sage member Dr Mike Tildesley told Times Radio that something is needed to bring the R number – reported last week to be between 1.1 and 1.3 – down to below 1.0, meaning the virus will no longer be growing.

He said: “What looks like is going to happen is possibly a slight delay to the start of term, and then ramping up mass testing to ensure that we rapidly detect cases – not just people showing symptoms but also asymptomatic cases so we can rapidly isolate children.”

Steve Chalke, founder of Oasis, one of the largest multi-academy trusts in England, also suggested delayed reopening.

He told the Today programme: “We would suggest a week or two’s delay to think it through, to do it well – and we think that if you really care about kids you would do this well – to invest now, to give time now makes sense.”

We do feel that we want our school to be open, and we are equally concerned by the impact of uncertainty on the pupils

A meeting was held between ministers, Downing Street officials and the Department for Education (DfE) on Monday to discuss the plan further, but the DfE would not comment on its outcome.

Downing Street said the Government is “still planning for a staggered opening of schools” after Christmas, but is keeping the plan under constant review.

The Prime Minister’s official spokesman told a Westminster briefing: “We’re still planning for a staggered opening of schools and we are working to ensure testing is in place.

“As we have said throughout the pandemic, we obviously keep all measures under constant review.”

Mary Bousted and Kevin Courtney, the joint general secretaries of the National Education Union (NEU), have also written to Education Secretary Gavin Williamson, as well as Mr Johnson, reiterating calls for schools and colleges to remain closed for at least the first two weeks of January, except for vulnerable children and the children of key workers.

Chris Foley, headteacher at St Monica’s RC High School in Prestwich, Manchester, said it is a “huge challenge getting the balance right between supporting pupils’ wellbeing and reducing community transmission”.

He told the PA news agency: “We do feel that we want our school to be open, and we are equally concerned by the impact of uncertainty on the pupils.

“We have wonderful Year 11 pupils who just want to get on with their studies, take their exams and then move on to the next stage of their life.

“The disconnect between national policy and then the delivery of policy directives at a school level has been the most challenging part of this, to be honest.”