Dozens of MPs have written to the Government to warn that plans to reform fire-safety regulations post-Grenfell will “put lives at risk” by allowing building materials to be approved without undergoing rigorous testing.

In a letter seen by The Independent, nearly 50 MPs from Labour, the Conservatives, the Liberal Democrats and the Green Party said that a refusal to rule out the use of desktop assessments to determine if cladding and other materials are safe was “unfathomable” and would contribute to a “culture of cost-cutting”.

The letter follows confirmation that ministers are to consult on allowing the continued use of the assessments, despite pledges in the wake of the Grenfell disaster to make safety regulations “as effective as possible”.

Desktop assessments have been used by manufacturers and construction companies in recent years as a way to bypass more comprehensive and expensive methods of testing.

The studies use data from previous assessments to clear combustible materials for use on high-rise residential buildings.

Some experts have warned that this results in corners being cut and inadequate testing of potentially lethal materials.

Fears have been raised that flammable cladding and insulation used on Grenfell Tower, which led to fire engulfing the entire building within minutes, had only been declared after undergoing desktop studies. Many of the materials were later found to fail fire safety tests.

Last week it was revealed that a fire door in the tower that was supposed to be fire-resistant for 30 minutes actually blocked the flames for only half that time.

Despite concerns over their effectiveness, construction firms have lobbied for desktop studies to continue to be allowed.

Reports suggest the Government is now planning to “revise the wording” on the use of desktop studies in a key document, known as Approved Document B, that explains how companies should meet safety regulations. A Government source confirmed to The Independent that the continuing use of desktop studies will be allowed, but said their use would be tightly regulated.

The confirmation prompted the 47 MPs to warn that the use of desktop studies should be banned completely in relation to flammable materials.

In Pictures: Grenfell Tower after the fire Show all 51 1 /51 In Pictures: Grenfell Tower after the fire In Pictures: Grenfell Tower after the fire Police have released images from inside the tower where at least 58 people have died Metropolitan Police In Pictures: Grenfell Tower after the fire A still from a video shared by polices what appears to be a stationary bicycle sitting among the ashes In Pictures: Grenfell Tower after the fire A still from a video shared by police shows the remnants of a burnt-out bathroom In Pictures: Grenfell Tower after the fire Picture showing the lifts on an unknown floor Metropolitan Police In Pictures: Grenfell Tower after the fire Emergency crews outside the front entrance to the tower Metropolitan Police In Pictures: Grenfell Tower after the fire Fire crews inspecting flats in the burnt out tower London Metropolitan Police In Pictures: Grenfell Tower after the fire Grenfell Tower is seen in the distance PA In Pictures: Grenfell Tower after the fire A drone flies near the scene of the fire which destroyed the Grenfell Tower block REUTERS/Stefan Wermuth In Pictures: Grenfell Tower after the fire 'Theresa May Stay Away' message written on the messages of support at Latymer Community Church for those affected by the fire Ray Tang/REX In Pictures: Grenfell Tower after the fire An aerial view of the area surrounding Grenfall tower Getty In Pictures: Grenfell Tower after the fire Donated shoes sit in the Westway Sports Centre near to the site of the Grenfell Tower fire Getty Images In Pictures: Grenfell Tower after the fire Messages of support for those affected by the massive fire in Grenfell Tower are displayed on a well near the tower in London AP In Pictures: Grenfell Tower after the fire A local resident stands on her balcony by the gutted Grenfell Tower in Latimer Road Getty Images In Pictures: Grenfell Tower after the fire Messages of condolence are left at a relief centre close to the scene of the fire that broke out at Grenfell Tower, EPA In Pictures: Grenfell Tower after the fire A police officer stands by a security cordon outside Latimer Road station Getty Images In Pictures: Grenfell Tower after the fire Firemen examine the scorched facade of the Grenfell Tower in London on a huge ladder AP In Pictures: Grenfell Tower after the fire A search dog is led through the rubble of the Grenfell Tower in London as firefighting continue to damp-down the deadly fire AP In Pictures: Grenfell Tower after the fire Labour leader Jeremy Corbyn comforts a local resident (name not given) at St Clement's Church in west London where volunteers have provided shelter and support for people affected by the fire at Grenfell Tower David Mirzoeff/PA In Pictures: Grenfell Tower after the fire Labour leader Jeremy Corbyn hugs councillor Mushtaq Lasharie as he arrives at St Clement's Church in Latimer Road, where volunteers have provided shelter and support for people affected by the fire at Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire Labour leader Jeremy Corbyn meeting staff and volunteers at St Clementís Church in Latimer Road David Mirzoeff/PA In Pictures: Grenfell Tower after the fire Firefighters with a dog walk around the base of the Grenfell Tower REUTERS/Peter Nicholls In Pictures: Grenfell Tower after the fire Emotions run high as people attend a candle lit vigil outside Notting Hill Methodist Church near the 24 storey residential Grenfell Tower block in Latimer Road, West London Getty Images In Pictures: Grenfell Tower after the fire Debris hangs from the blackened exterior of Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire A woman speaks to Mayor of London Sadiq Khan outside Notting Hill Methodist Church near Grenfell Tower in west London after a fire engulfed the 24-storey building Yui Mok/PA Wire In Pictures: Grenfell Tower after the fire A woman holds a missing person posters near the Grenfell Tower block REUTERS/Stefan Wermuth In Pictures: Grenfell Tower after the fire Sadiq Khan speaking with a resident James Gourley/REX In Pictures: Grenfell Tower after the fire Ken Livingstone walks near the scene of the Grenfell Tower fire Getty Images In Pictures: Grenfell Tower after the fire Mayor of London Sadiq Khan is confronted by Kai Ramos, 7, near Grenfell Tower in west London after a fire engulfed the 24-storey building Yui Mok/PA Wire In Pictures: Grenfell Tower after the fire Mayor of London Sadiq Khan speaks to a woman outside Notting Hill Methodist Church near Grenfell Tower Yui Mok/PA Wire In Pictures: Grenfell Tower after the fire Volunteers distribute aid near Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire Family and friends of missing Jessica Urbano, 12, wearing photographs of Jessica pinned to their t-shirts gather near Grenfell Tower EPA In Pictures: Grenfell Tower after the fire Family and friends of missing Jessica Urbano, 12, wearing photographs of Jessica pinned to their t-shirts gather near Grenfell Tower EPA In Pictures: Grenfell Tower after the fire Family and friends of missing Jessica Urbano, 12, wearing photographs of Jessica pinned to their t-shirts gather near Grenfell Tower EPA In Pictures: Grenfell Tower after the fire People attend a vigil at Notting Hill Methodist Church near Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire People gather to observe a vigil outside St Clement's Church following the blaze at Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire People light candles as they observe a vigil outside St Clement's Church following the blaze at Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire People attend a vigil at Notting Hill Methodist Church near Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire A man distributes food from the back of a van near the scene of the fire which destroyed the Grenfell Tower block REUTERS/Paul Hackett In Pictures: Grenfell Tower after the fire A firefighter is cheered near the scene of the fire which destroyed the Grenfell Tower block REUTERS/Paul Hackett In Pictures: Grenfell Tower after the fire A T-shirt with a written message from the London Fire Brigade hangs from a fence near The Grenfell Tower block REUTERS/Stefan Wermuth In Pictures: Grenfell Tower after the fire A young girl on her way to lay flowers near Grenfell Tower Getty Images In Pictures: Grenfell Tower after the fire The remains of residential tower block Grenfell Tower are seen from Dixon House a nearby tower block Getty In Pictures: Grenfell Tower after the fire Volunteers prepare supplies for people affected by the Grenfell Tower block which was destroyed in a fire REUTERS/Neil Hall In Pictures: Grenfell Tower after the fire Volunteers move a car to make space for a lorry picking up supplies for people affected by the Grenfell Tower block REUTERS/Stefan Wermuth In Pictures: Grenfell Tower after the fire People distribute boxes of food near the scene of the fire which destroyed the Grenfell Tower bloc REUTERS/Paul Hackett In Pictures: Grenfell Tower after the fire A woman touches a missing poster for 12-year-old Jessica Urbano on a tribute wall after laying flowers on the side of Latymer Community Church next to the fire-gutted Grenfell Tower AP In Pictures: Grenfell Tower after the fire A man looks at messages written on a wall near the scene of the fire which destroyed the Grenfell Tower block REUTERS/Paul Hackett In Pictures: Grenfell Tower after the fire Candles and messages of condolence near where the fire broke out at Grenfell Tower EPA In Pictures: Grenfell Tower after the fire Police carry a stretcher towards Grenfell Tower Rick Findler/PA Wire In Pictures: Grenfell Tower after the fire Emergency services at Grenfell Tower Rick Findler/PA Wire In Pictures: Grenfell Tower after the fire Police carry out a body from Grenfell Tower in west London after a fire engulfed the 24-storey building Rick Findler/PA Wire

In a letter to Housing and Communities Secretary Sajid Javid, they wrote: “In the wake of the Grenfell Tower fire we find it unfathomable that the Government’s response would be to make building regulations weaker and more lenient when it comes to the use of combustible materials on high rise buildings and tower blocks.

“We are deeply concerned about the culture of cost-cutting and unsafe practices that came to light post-Grenfell, and we await the publication of Dame Judith Hackitt’s review of building safety regulations.”

In December, an interim report of an independent review into building regulations carried out by Dame Judith Hackitt said the Government should “significantly restrict the use of desktop studies” to ensure “they are only used where appropriate and with sufficient, relevant test evidence.”

In their letter, the MPs said: “The Hackitt Review’s interim report called on the Government to ‘significantly restrict’ the use of desktop studies to approve changes to cladding, and we urge you to ensure that the Government will not make any changes to regulations that could result in combustible materials being cleared for use on tower blocks in our constituencies without a fire test taking place.

“Such changes would be totally unacceptable, highly dangerous and would put lives at risk.

“We call on you to be true to your promises and ensure that no changes are made to fire safety and building regulations that could make another tower block fire more likely.”

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Labour MP David Lammy, who lost a friend in the Grenfell Tower fire and co-ordinated the letter from MPs, said: “I am frankly shocked that the Government are even considering desktop studies.

“Sajid Javid promised us that the Government will take every precaution to avoid another tragedy, and he will be held to that promise.”

A number of groups have voiced doubts about the effectiveness of desktop studies.

In its submission to the Hackitt Review, the Local Government Association said of the method: “These reports are a matter of judgement and cannot be verified by building control.

“Subsequent to the Grenfell Tower fire a number of cladding systems which have been used on tall buildings have proved not to meet the required standard of non-combustibility.

“This raises serious questions about the appropriateness of a route to compliance which does not depend on an actual fire test.”

In another submission, the Royal Institute of British Architects said the safety of building materials should “be based on full scale fire testing and not use desktop studies”.

And the National Fire Chiefs Council warned: “Another concern is the practice of undertaking desktop studies in the absence of carrying out fire tests ... This relies heavily on the competence of the person undertaking the desktop study, and may lead to errors or a reduction in safety margins.”

However, construction firms’ representatives have argued that desktop studies should continue to be allowed.

The Construction Industry Council said: “The need for desktop assessments is clear, particularly in the situation where requirements are made more stringent ... The lack of capacity for large scale fire tests also makes the desktop assessments necessary.

“However, desktop assessments or judgements on extended application need to be of high quality, and carried out by competent professionals.”

Government sources insisted desktop studies were valid in certain circumstances and denied the proposed changes amount to a weakening of regulations.