IoS investigation: Revealed - the menace of UK's firetrap tower blocks

Building repairs have destroyed many safety features

Tragedy: Lakanal House in the Sceaux Gardens estate in Camberwell, south London, which caught fire in July 2009, killing six people (Rex Features)

Hundreds of thousands people living in high-rise flats around the UK face lethal fire risks because building work in ageing tower blocks has undermined the main safeguard designed to stop fires spreading out of control. Experts fear the safety flaws are not being properly investigated because of serious failings in the way buildings are inspected.

A leading fire-safety consultant warned of growing concern about safety standards and checks on similar blocks, saying confusion about the issue "could cost people's lives".

A fire in a south London tower block which killed six people, including three children, in 2009 revealed that refurbishment work carried out on the building had undermined its principal fire-protection system. A small fire in a faulty TV set on the ninth floor spread through several floors and along corridors, trapping many of the 84 families living there.

An inquest this week into the fire at Lakanal House in Camberwell will hear how work carried out by builders allowed flames to spread to the fifth, seventh and 10th floors. Its speed and unpredictability surprised experienced firefighters who had told residents they were safer in their flats than being evacuated. Firefighters were hampered by smoke in the building's single stairwell and a lack of layout plans. By the time they had the blaze under control, some 17 people needed hospital treatment for burns and smoke inhalation. The six who died were Dayana Francisquini, 26, and her two children, Thais, six, and Felipe, three; Helen Udoaka, 34, and her three-week-old daughter Michelle; and Catherine Hickman, 31.

A police-led investigation into the fire found that work carried out on the building destroyed its "compartment" protection: barriers designed to make sure any fire is contained in a single flat long enough for firefighters to put it out. Investigators found that firewalls designed to stop smoke and flames from spreading had been cut to allow pipes and duct work; ceiling and floor spaces lacked protection measures and vital flameproof materials had been removed.

Fire chiefs began a nationwide inspection of tower blocks, which revealed similar flaws. Nationally it is estimated there are 4,000 to 5,000 blocks of flats that are similar in age and construction to Lakanal House. In Birmingham, faults were found in more than 200 blocks. However, The Independent on Sunday has learned that many more fire threats still exist more than three years after the south London fire because of serious failings in the way buildings are assessed for dangers.

Many of the problems stem from the Decent Homes initiative, a well-intentioned Labour government scheme to improve social housing which greatly increased the dangers to residents. Refurbishments which improved the living conditions of tens of thousands of residents also made the dangers of fires spreading uncontrolled throughout flats worse. Workmen who were unaware of the safety implications of the work they were doing removed firewalls or modified them in ways that would allow fires to spread.

The problem is exacerbated by the fact that many assessments of at-risk buildings are carried out by inadequately qualified inspectors. Safety experts also warn that cutbacks in the fire service mean too few of the checks are being audited by experienced inspectors. Some landlords' fire-risk assessments "aren't worth the paper they are written on", one safety authority said yesterday.

The shadow fire minister Chris Williamson warned that "cutbacks in fire and rescue services will load more risks on the general public. I shudder to think to what the consequences of such cuts will be. It will be a matter of life and death – literally."

This week's inquest will hear that London Fire Control staff gave standard "stay put in your flat" advice to several residents on the higher floors who called for help. They insist the advice was given honestly and in the best interests of the residents based on the assumption normal protections would contain the fire long enough for them to deal with it.

While a subsequent investigation found that the repairs on the 50-year-old flats breached defences designed into the building by architects, the Crown Prosecution Service concluded last May there was insufficient evidence to convict any individual, company or council official of manslaughter.

Nevertheless, the tragedy led to safety reviews of similar high-rises across the country. "It isn't an exaggeration to say that tower block safety wasn't really on our radar before then," one experienced fire inspector said last week. "Prior to Camberwell, we had never had a major incident and few, if any, audits to check fire safety were carried out." Last year, more than 3,000 safety audits were carried out on tower blocks in England. The initial checks revealed hundreds of blocks where safety had been similarly compromised.

Fire chiefs insist many landlords, including local councils and housing associations, moved fast to rectify the worst problems, but privately they estimated only between a third and a half of all tower blocks had been correctly assessed. Many questioned the competence of those carrying out the assessments.

David Sibert, fire adviser to the Fire Brigades' Union (FBU) said: "The quality of too many fire-risk assessments remains poor. Too often they are carried out by people who lack appropriate knowledge. To do it properly it is necessary to get into the hidden parts of a building, behind walls and into ceiling spaces."

Since 2006, landlords are legally responsible for risk assessments, which should be checked by the fire service. A 2011 survey of housing professionals found only one in four thought they had carried out "suitable and sufficient" assessments. In the absence of government regulations, the fragmented fire prevention industry has been slow to agree competence benchmarks, publishing them only last October.

Ian Gough, a fire safety consultant and a former senior fire safety officer in Northamptonshire, said: "I don't think the Government at the time realised the full implications of the shift of some of the work that fire and rescue services used to do on to the private sector. It was naive to believe that the person responsible for the building would either be able to do it themselves, or know how to employ people to do it. The Government took few steps to prepare for it and so created an industry that is totally unregulated."