Potentially “hundreds more” schools across the country could be affected by unsafe concrete, the education secretary has said.

More than 100 schools across England have been told to partially or fully close just days before the start of term as a result of concerns over reinforced autoclaved aerated concrete (RAAC).

The building material was widely used from the 1950s to the mid-1990s but is now feared to be at risk of collapse.

Speaking to Nick Robinson on the BBC’s Today Programme, Gillian Keegan said an incident last month where a panel fell from a roof that had previously been assessed as non-critical prompted urgent action on RAAC.

She also said that potentially “hundreds more” schools could be affected by the crisis.

“The vast majority of surveys that we do, they come back without RAAC, but where we find it we will then treat everyone as critical and we will either prop them up or put temporary accommodation into place and then we will refurbish or rebuild them if they require that.”

The Department for Education has so far refused to say which schools are affected, but Ms Keegan said that a list of affected schools in England would be published this week.

The education secretary has faced criticism for her handling of the crisis, with one Conservative MP telling Sky News deputy political editor Sam Coates that “she either wasn’t across the detail or didn’t know schools would have to close”.

The unnamed MP also reportedly said: “This investigation on school structures has been going on for a while - I am gobsmacked the advice so quickly and brutally performed a handbrake turn. Keegan needs to be transparent.”

In an interview with Sky News this morning, Ms Keegan announced plans for 239 school rebuilding projects, which would be completed “as soon as possible”.

“We’ve delivered much better value for money, many more schools have been rebuilt, many more schools are going to be rebuilt - we’ve got a grip of RAAC.”

One school in Horsham will be closed tomorrow due to concerns over the concrete, with another school in East Sussex undergoing inspection.

Gillian Keegan has been approached for comment.