Fewer than one in six new schools have been built with sprinkler systems installed, ministers have admitted, in findings branded “absolutely terrifying” by union officials.

Despite official government guidance that all new schools should have sprinklers “except in a few low-risk schools,” figures uncovered by the Labour party showed that, of the 673 schools built under the government’s flagship school building scheme and free school programmes, sprinklers were fitted in just 105.

The official figures also suggested that just one in 15 free schools approved by the government had been built with sprinklers – a far lower rate than other types of schools.

Labour warned that the lack of sprinklers was putting children and staff at unacceptable risk. There have been more than 7,000 fires at educational premises in the last decade. Stephanie Peacock, the Labour MP who unearthed the figures, said: “It beggars belief that we even have to debate having the highest standards of fire safety in schools but clearly that is yet another victim of this government’s obsession with austerity.”

Nadine Houghton, national officer for schools at the GMB trade union, said the revelations were “absolutely terrifying” and demanded urgent action. “How can we trust ministers with our safety when they have a shameful track record of fighting to remove a requirement for new schools to be protected by installing sprinklers?” she said. “Money that is spent on dealing with the aftermath of fires should be being spent on basic prevention such as sprinklers.”

The figures covered almost 700 schools built and approved under the Priority Schools Building Programme, which dates back to 2011.

A Department for Education spokesperson said: “The safety of pupils and staff in our schools is paramount. Schools are fundamentally safe places and are designed to be evacuated as quickly as possible. All schools are required to have an up-to-date fire risk assessment and to conduct regular fire drills. All new school buildings must be signed off by an inspector to certify that they meet the requirements of building regulations and where sprinklers are considered necessary, they must be installed.”