Ministers remain under pressure to spell out their plans to make schools safe from aerated concrete after dozens more schools have been found to contain the potentially dangerous material.

The Department for Education on Tuesday added 27 new schools to the list of those with reinforced autoclaved aerated concrete (Raac) on their premises, taking the total to 174 schools in England.

Raac is a type of crumbling type of concrete that was widely used in the second half of the 20th century. Experts warn the material is likely widespread throughout the public sector, with private businesses also likely plagued.

Politicians are facing difficult questions about how some buildings that still form part of the nation’s vital infrastructure were erected in the 1960s with roofs designed to last just 30 years.