The publication of the Grenfell Tower inquiry 's first report has been delayed until October.
Core participants, including survivors and those who lost relatives in the deadly blaze, were expecting it would be released this spring.
But 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".
It said: "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."
The report follows the first phase of the inquiry, which is limited to what happened on the night of 14 June 2017 when fire ripped through the west London tower block, killing 72 people.
Caroline Featherstone, solicitor to the inquiry, said in the letter that plans for the second phase are continuing and it is still due to go ahead in January 2020.
Natasha Elcock, chairwoman of Grenfell United , the group for survivors and bereaved families, said: "It's disgraceful the inquiry have underestimated the complexity of the evidence that was produced in Phase 1 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."