Eight unions representing teachers and school workers, as well the body for governors, have written to Rishi Sunak demanding an extra £4.4bn annually to ensure buildings are safe for children in England.

They say the crisis involving reinforced autoclaved aerated concrete (Raac), which has cast a shadow over the start of the term and has been found in 174 schools in England so far, has exposed the chronic underfunding of school buildings in recent years.

Unions say many are unsafe and not fit for purpose. The additional funding would bring total annual investment in the ageing school estate up to £7bn, which is what officials at the Department for Education (DfE) have previously recommended.

The deteriorating condition of the school estate has long been a concern, but the DfE has failed to secure necessary funding from the Treasury. The unions are hoping the decision by Gillian Keegan, the education secretary, to suddenly close all school buildings with Raac before the start of the autumn term will force the chancellor to stump up more cash in his autumn statement on 22 November.

Unions met Keegan last week but are concerned there is still no timeframe for when all schools at risk from Raac will be investigated by structural engineers and no deadlineto clear Raac from every school.

While the lifespan of Raac was known for years, and the potential risks, the alert followed a series of sudden failures of Raac-built structures in recent months, which forced large numbers of headteachers and schools to make alternative arrangements.

The union letter says: “Parents, school staff and children and young people have been alarmed to hear – at the start of the new academic year – about crumbling school buildings and the deterioration of the school estate, which could present a very serious risk to their safety.

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