Government guidance on fire safety in school buildings is being ignored in the “rush to build new schools as cheaply as possible”, it has been claimed.

Current guidance on new school builds – the Building Bulletin 100 document – states that all new schools, with the exception of a few low-risk schools, should have sprinklers fitted.

However, since 2010, only 35 per cent of new schools have been fitted with sprinklers.

The National Union of Teachers (NUT), Fire Brigades Union (FBU) and Association of Teachers and Lecturers (ATL) have written to education secretary Justine Greening raising the issue.

The letter also seeks confirmation that the government is to abandon its plans to allow new schools to be built without sprinkler systems.

The DfE had been proposing to revise the Building Bulletin to remove the expectation that sprinklers be installed. However,

The Observer reported last month that the plan is being quietly dropped.

The draft guidance has been removed from the Department for Education (DfE) website as government departments were reportedly told to look again at fire safety in the aftermath of the Grenfell Tower tragedy.

The draft guidance had included a statement that sprinklers were not required to “achieve a reasonable standard of life safety” and that there would be “no expectation” that most new school buildings should have them.

In a Parliamentary debate on the issue last year, schools minister Nick Gibb said that having sprinklers in new school buildings added between two and six per cent to the cost of construction.

The unions’ letter to Ms Greening seeks official confirmation that the revision is to be dropped. The letter states: “It was grossly irresponsible for any government to have brought forward such proposals in the first place. Without the appalling Grenfell Tower tragedy we consider it highly likely that the revised and watered-down Building Bulletin would have become the Department’s official advice, with potential dire consequences for health and safety in our schools.”

The letter adds: “You will be aware that even with the sprinkler ‘expectation’ in place, only 35 per cent of new schools were fitted with sprinklers between 2010 and 2016. This can be contrasted with 70 per cent between 2007 and 2010. Can you please explain why there was such a drop-off over these years?

“It seems likely that the change of government in 2010 led to the sprinkler ‘expectation’ being taken less seriously by those responsible for building schools, because of the desire to build new schools cheaply.”

In a press statement last week, the three unions said: “It is clear that current guidance is being ignored in the rush to build new schools as cheaply as possible.”

The unions’ letter is also seeking clarification over the use of flammable cladding in school builds. The current Building Bulletin guidance discourages its use and the unions are now using Freedom of Information requests to uncover information on how many schools have been fitted with such cladding.