The Department for Education has informed East Sussex County Council that one school in the area was at least partially built with reinforced autoclaved aerated concrete (RAAC).

The school, which has not been named, is now undertaking an “urgent inspection” and reviewing if any parts of the building need to be closed.

Schools in Brighton and Hove and West Sussex are understood to be unaffected by the issue.

A spokesman for East Sussex County Council said: “East Sussex County Council has been informed by the Department for Education that there is one school in the county that has unsafe concrete.

“The school is undertaking an urgent inspection of the site and reviewing whether any parts of the building need to be closed.

“Further details are not available until the school has informed families about any changes for the new term next week.”

More than 100 schools and colleges have been told by the Department for Education to partially or fully close buildings just days before pupils prepare to return after the summer holidays.

Schools built between 1930 and 2000 which are maintained by West Sussex County Council are to undergo a physical inspection following fears over the concrete.

Education Secretary and MP for Chichester Gillian Keegan said: “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.

“We must take a cautious approach because that is the right thing to do for both pupils and staff.

“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.”

Peter Kyle, Labour MP for Hove, described the situation as “shocking evidence of a department in disarray”.

He said: “There’s just hours to go before the start of the new term and despite knowing about the potential risks posed by RAAC for months, Conservative ministers are now phoning schools to ask them if they are ready to close, further disrupting children’s education.

“I am thinking of all the children who are excited about entering Year 7 and how that thrill is now tarnished with worry and fear.

“The Education Secretary needs to tell parents just what on earth is going on.”