The Grenfell Tower Inquiry’s first report will not be published until October – months after survivors expected its release.
In a letter obtained by the Press Association they were told on Friday that writing the report “has proved to be a far more complex and time-consuming task than the Inquiry had originally anticipated”.
Groups representing survivors and families of the 72 people killed in the June 14 2017 blaze criticised the move, with one branding the delay “disgraceful”.
The report, which follows the first phase of the inquiry, will focus on what happened on the night of the fire and was expected to be published in spring.
The inquiry’s core participants, including survivors and those who lost relatives in the blaze, were expecting it would be released this spring – before the second anniversary of the disaster.
But Caroline Featherstone, Solicitor to the Inquiry, said in the letter: “The chairman will be in a position to write to the Prime Minister with his final report after the parliamentary recess for publication most likely in October.”
Natasha Elcock, chair of Grenfell United, the survivors and bereaved family group, said: “It’s disgraceful the inquiry have underestimated the complexity of the evidence that was produced in phase one and have further delayed the report until autumn.
“That we are only finding this out now, when we were expecting the report to be published ahead of the two-year anniversary, shows how they continue to disregard survivors and bereaved through this process.”
The letter said the report will set out in detail what happened on the night of the blaze.
“That involves an almost minute-by-minute description of how the fire started, how it spread and what was happening on each floor of the Tower,” it said.
“It also involves a detailed description and analysis of what was happening in the incident control room and on the ground, as well as the response of the emergency services and relevant organisations.”
Inquiry chairman Sir Martin Moore-Bick has previously said he does not consider it appropriate to make interim recommendations ahead of the report and any recommendations the chairman does make will be limited to the first phase.
But some survivors have become frustrated that safety recommendations, such as abandoning the “stay-put” policy for buildings over 10 storeys, are so far yet to be implemented.
Ms Elcock said: “It appears, despite everything survivors and bereaved said in the weeks after the fire, the inquiry has woefully underestimated the catastrophic complexity and scale of the failures that led to Grenfell.
“They also continue to woefully underestimated the needs of bereaved and survivors.”
The letter said that plans for the second phase of the inquiry, which will examine the lead up to the blaze, including the refurbishment of the tower, are continuing and it is still due to go ahead in January 2020.
Last year, Scotland Yard said no criminal charges will be brought until the end of the inquiry, which will be at the earliest in 2021.
The latest delay will add to the wider dissatisfaction among survivors to the inquiry process.
Justice 4 Grenfell, a campaigning group for those affected by the fire, said: “This has only served to decrease bereaved, survivors and residents’ (BSR’s) confidence in the process further.
“They have already raised the issues of a lack of transparency during the inquiry and a culture of secrecy and exclusion.
“This is another excuse on a long list of shifting the parameters of the inquiry and a lack of willingness to discuss with BSRs how and why decisions are made.”
“We want the inquiry and the criminal investigation to be thorough and to get to the truth, but there must be no more delays.
“We are living in a limbo, increasingly frustrated and we need to know there will be some resolution soon. A slow justice is a painful justice for all of us.”
The letter also said the inquiry’s new venue, which will be moved to west London after concerns were raised about the location and lay out of the hearing room in Holborn Bars, central London, will be announced at the end of the month.
Elizabeth Campbell, leader of Kensington and Chelsea Council, said: “This news will be very disappointing to the families and the communities in our borough.
“We all want to get to the truth of what happened nearly two years ago, and we hope the inquiry can still move forward despite the delay to this report.
“I want to reiterate that our approach to the inquiry has been to provide the witnesses they have asked for and the documents they require. We are serious about our role in making sure a tragedy like this never happens again.”