LONDON — Some of the 72 people who died in the Grenfell Tower fire in 2017 would have survived if firefighters and emergency operators had not told them to stay in their apartments, according to a government report to be released on Wednesday.

The 1,000-page report, which comes more than two years after the deadliest fire in recent British history, is harshly critical of the London Fire Brigade, calling it dangerously unprepared for such a tragedy, according to multiple British news organizations that gained access to the conclusions before their release.

The fire on June 14, 2017, began on the fourth floor of the 24-story building and spread rapidly upward because of flammable exterior cladding and insulation that had been added to the building the year before.

Those outer layers would not have been allowed on a high-rise in many countries, including the United States, because of the fire danger they posed.