Top government officials have been urged to “come clean” about the scale of the problems facing England’s school buildings, as thousands of pupils face a disrupted start to term.

More than 100 schools and colleges have been told to partially or fully close buildings because of fears concrete in the foundations could suddenly collapse.

The Department for Education (DfE) said some children may be forced back into pandemic-style remote learning.

However, the Government has refused to publicly reveal the 104 education facilities that have been told to shut buildings, and critics warned the problems with reinforced autoclaved aerated concrete (RAAC) could be far wider.

Education Secretary Gillian Keegan told broadcasters: “Most parents should not be worried about this at all.”

But shadow education secretary Bridget Phillipson said: “We haven’t seen the full list of schools affected. We don’t know where they are, ministers should come clean with parents and set out the full scale of the challenge that we’re facing.”

Official guidance was issued to schools, school nurseries and colleges – which have been told they will have to fund their own emergency accommodation.

The DfE said it contacted 104 schools in the wake of an analysis of new cases after 52 of the 156 educational settings containing the concrete took protective steps so far this year.

The department said a “minority” will need to “either fully or partially relocate” to alternative accommodation while safety measures are installed.

But its guidance to schools said funding will only be provided for works that are “capital funded” and schools will have to pay for rental costs for emergency or temporary accommodation.

Space in nearby schools, community centres or in an “empty local office building” was recommended for the “first few weeks” while buildings are secured with structural supports.

Schools were told moving to pandemic-style remote education should only be considered as a “last resort and for a short period”.

Calling for all affected schools to be named, Ms Phillipson told BBC’s Newsnight: “I expect ministers next week in the House of Commons to publish that data and tell parents and tell the public exactly where the problems are.”

RAAC is a lightweight building material used from the 1950s up to the mid-1990s, but now assessed to be at risk of collapse.

The DfE has been considering RAAC as a potential issue since late 2018 but the timing of the decision to issue guidance just days before the start of term has angered unions.

National Education Union general secretary Daniel Kebede said: “It is absolutely disgraceful, and a sign of gross Government incompetence, that a few days before the start of term, 104 schools are finding out that some or all of their buildings are unsafe and cannot be used.

“To add insult to injury the Government states in its guidance that it will not be covering the costs of emergency temporary accommodation or additional transport.”

Which schools are affected?

The BBC say affected schools include Ferryhill School, a secondary in County Durham, Willowbrook Mead Primary Academy in Leicester and Corpus Christi Catholic Primary School in Brixton, south London.

Other schools suspected of containing RAAC will be surveyed in a matter of weeks.

If RAAC is confirmed, the DfE has promised that “appropriate rapid action is taken” which could include funding to remove any immediate risks and, where necessary, arranging temporary buildings to be put in place.

The Unison union’s head of education Mike Short said: “Parents, pupils and staff will be relieved the issue is finally being taken seriously.

“But to wait until the eleventh hour as schools are preparing for a new academic year will create turmoil for thousands of families. And this could just be the tip of the iceberg.”

The state of England’s school buildings – as well as problems with RAAC – were highlighted in a report in June by public spending watchdog the National Audit Office (NAO).

The NAO’s report said 700,000 pupils were learning in schools that required major rebuilding or refurbishment.

Paul Whiteman, general secretary of school leaders’ union NAHT, said the “timing of this couldn’t be worse”.

“What we are seeing here are the very real consequences of a decade of swingeing cuts to spending on school buildings,” he said.

The general secretary of the teaching union NASUWT said the announcement highlighted “more than a decade of wilful under-investment” in schools.

Dr Patrick Roach said: “Although we welcome that the DfE has finally taken action to safeguard pupils and teachers, it would appear that mere luck rather than judgment has prevented a major disaster from occurring.”

The Education Secretary insisted that a “cautious approach … is the right thing to do for both pupils and staff”.

“Nothing is more important than making sure children and staff are safe in schools and colleges, which is why we are acting on new evidence about RAAC now, ahead of the start of term,” she said.

“The plan we have set out will minimise the impact on pupil learning and provide schools with the right funding and support they need to put mitigations in place to deal with RAAC.”