In one of the classrooms of Gillotts secondary school in Henley-on-Thames, there is a mysterious, acrid smell. It is a school day but the room is empty because this “awful” scent, a mix of damp and chemicals, clogs children’s throats and clings to the teachers’ hair and clothes long after they go home.

“That classroom is shut and unusable because of the smell – and I could really do with that classroom,” said headteacher Catharine Darnton. Her state school has 900 pupils and, like many other heads across the country, she has struggled to maintain her dilapidated building in the face of the government’s austerity cuts. As well as the stink, heating failures and electricity blow-outs have led to partial temporary closures of the school and blocked drains have threatened to leak raw sewage onto the playground. Darnton has been forced to take money intended for the education of students and allocate it to repairs and even capital expenditure. The low point came when, in winter, the building was so cold and dark she had to consider closing the school. “It was insane,” she said.

Facebook Twitter Pinterest Gillotts is among the quarter of schools that do not believe their buildings are in a good state of repair. Photograph: Antonio Olmos/The Observer

Last week, a survey of 3,500 teachers revealed two-fifths of schools have set up buckets to catch drips when it rains and over a quarter do not believe their schools are in a good state of repair. The research, by the survey app Teacher Tapp in collaboration with Schools Week, found that teachers working in schools built in the mid-20th century were the most likely to report using buckets – but even in schools built in the 2010s, around 27% of teachers still reported having to resort to this tactic.

Theresa Madden is among the many headteachers who have learnt to dread bad weather: “When it rains, I worry about where the building will burst at the seams.” She teaches at St John Fisher Catholic College, a comprehensive school in Staffordshire. Despite achieving “excellent” outcomes for her students, Madden said “years of underfunding mean we are reactive rather than proactive to repairs. We receive just over £20,000 in capital funding annually which we could spend tenfold on repairs alone, before we even consider small projects. It is shameful the government fails to recognise that underfunding means young people are receiving an education akin to 50 years ago.”

Darnton, like Madden, is calling on the government for more capital investment. Gillotts was one of five schools in Oxfordshire designated for a full rebuild under Labour, but this was cancelled after Michael Gove axed the Building Schools for the Future programme in 2010. The school’s capital budget used to be about £80,000 a year, but was cut by 80% to £18,000 in 2011 and has stayed at that level ever since. Also, funding per pupil has remained the same (around £4,700) between 2012 and 2018: a cumulative 16% cut after inflation is taken into account.

The terrible stink first emerged in classroom X2 when a 40-year-old leaky pipe caused a huge heating failure. Even after further leaks partly closed the school, the government’s central improvement fund repeatedly refused applications to fully repair the school’s disintegrating underground heating system, landing Darnton with a £30,000 bill and effectively wiping out her year’s planned maintenance budget. While she was trying to find funds to repair the leak, the smell got worse.

By not maintaining our schools, we are storing up problems and the cost is higher when we have to do it in an emergency. Catharine Darnton, Gillotts headteacher

Now the heating is fixed but she has been forced to allocate £11,000 for air tests and underground drilling to try to get rid of the stench, and still cannot use the classroom. It may have be demolished and rebuilt – and that is not the only significant expense Darnton is facing this year. In December, a blocked drain threatened to send raw sewage back up through the school’s pipes. After repeatedly paying £1,500 to clear it, Darnton is now facing a bill of around £50,000 to keep sewage out of her playground.

Most of this colossal expense, she says, could have been avoided if the school had been able to afford to line its drains, as it was advised to do, a few years earlier. “By not maintaining our schools, we are storing up problems and the cost is higher when we have to do it in an emergency,” she said.

What upsets her most is the government’s lack of respect for heads, who are speaking out. “The government mantra is that there has never been more money for education. It doesn’t matter to me how much money there is across the system. What I see is that I’ve had real terms cuts to my funding every year.” She is working 70-hour weeks, trying to make do with the current level of funding. “I can’t go on doing that. I’m desperate for my capital funding to be reinstated.”

A Department for Education spokesperson said: “We have allocated £6bn in capital funding to maintain and improve ... school buildings since 2015, which includes an additional £400m for schools in 2018-19.

“In addition, our Priority School Building Programme is rebuilding or refurbishing over 500 schools across the country, and we have reduced delivery timescales and driven down the costs of building schools. As the National Audit Office said in its report from February 2017, the Priority School Building Programme has delivered schools around a third cheaper than Building Schools for the Future.”“We are updating our information on the condition of state-funded schools in England, so that we can carry on targeting funding.”