The next phase of the inquiry is expected to focus on the underlying cause of the disaster: flammable exterior cladding and insulation that allowed the fire to engulf the tower quickly. The cladding is not allowed in high-rise buildings in various countries, including the United States, and investigations after the fire concluded that it did not meet British safety standards.

“All we could see was blame against the brave firefighters, who saved my family’s life,” Asma Kazmi, a survivor of the fire, said in October when the report was published.

But many families viewed the firefighters and their leader quite differently. Last month the relatives of 20 people who died in the fire sent a letter to Mayor Sadiq Khan of London asking for the resignation of Ms. Cotton, whom they called “incompetent.”

The blaze began at 12:50 a.m. on June 14, 2017, on the fourth floor of the 24-story tower. Like most modern high-rises, it had a concrete structure that was designed to keep any fire compartmentalized, but instead the flames spread rapidly across the exterior, a phenomenon that caught firefighters off guard.

Ms. Cotton, the first woman to lead the London Fire Brigade, served as a firefighter in London for 32 years. She called the Grenfell Tower fire the worst the brigade had experienced.

“The brigade has and will keep making the changes it can make and continue its fight for all of the other changes that are needed, to prevent such a terrible incident and loss of life from happening again,” she said in her statement.

Groups of survivors have accused the government of not enacting lessons learned from the fire. Thousands of people still live and work in buildings wrapped in the type of cladding that fed the inferno.