Responding to a question from Labour Assembly Member Tom Copley at Mayor's Question Time on Thursday July 13, Sadiq Khan labelled the council "inept and incompetent and close to being useless".
The strong wording was in response to a question about how support given to victims of the fire may have improved.
Mr Khan went on to say that not only was the support provided bad to begin with, but that four weeks on from the devastating fire, there is still very little council support.
This adds to his comments about the rehousing of Grenfell residents, as he told the assembly that the deadline given to move all displaced residents of the ill-fated tower block to temporary or long term housing was badly missed.
The Mayor said the deadline of three weeks to rehouse the survivors was not met, with just three households moving to new accommodation by that time period.
"They [the council] have been missing in action and failed to provide residents the support they need," said Mr Khan.
"Kensington and Chelsea Council can rely upon other councils for help but they took too long to ask for it.
"Confidence in the council has gone and I am not sure it will be gained by the new leader.
"The government could have sent in commissioners to take over the council but instead a back room deal was hatched up."
He was also keen to stress that the 69 homes the government set aside for Grenfell victims were already intended to be for social housing, meaning the original intended recipients would have to wait even longer to be housed.
Responding to an earlier question about the lessons to be learned from the June 14 fire which has claimed at least 80 lives, the mayor demanded that there be an interim report this summer.
An Assembly Member pointed out that measures like retro-fitting sprinklers to tower blocks, revisiting regulations around cladding and an examination of advice given to residents were all highlighted in the inquest into the 2009 Lakanal House tower block fire, published in 2013.
The Mayor asked the government to ensure an interim report with recommendations to councils for tower block safety was published this summer to ensure they are acted upon and not ignored.
"For those that speak pejoratively of red tape, heath and safety and about regulations, Grenfell is the consequence of reducing health and safety, red tape and good quality regulations," said the Mayor.
Kensington and Chelsea Council has been approached for comment.
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