Baby P died after suffering months of abuse
The local authority in which Baby P died was able to "hide behind" false data and mislead an Ofsted team, the inspection agency's head has claimed.
Haringey Council received a "good" rating from Ofsted just weeks after the 17-month-old's death.
Christine Gilbert told the Guardian mistakes were made, but said inspectors had been given incorrect data.
A Haringey Council spokesman said the authority was in contact with Ofsted about the detail of their findings.
He added: "We will take whatever action is necessary as part of the review of child protection arrangements in Haringey now being carried out."
Welfare professionals visited Baby P 60 times before he died in August 2007.
Opposition Liberal Democrat councillors in Haringey have claimed that a damning report into the case will not be up for discussion at a council meeting on Tuesday.
'Catalogue of concerns'
Baby P, who cannot be named for legal reasons, suffered more than 50 injuries at the hands of his mother, 27, her boyfriend, 32, and their lodger, Jason Owen, 36.
The three were convicted of causing or allowing the death of a child and will be sentenced in the spring.
Ms Gilbert told the newspaper that, during the 2007 inspection, Haringey managers wrongly claimed they had assessed children.
A subsequent review found that the assessments were incomplete and had been carried out in breach of procedures.
"I think that if the grades we gave last December gave a false assurance we have to take responsibility for that," she said.
"I'm absolutely not washing my hands of it."
The report of the joint area review into Baby P's death, which will not be made public, was "devastating", she told the newspaper.
"By the second day the inspectors were saying the things they were finding were really inadequate," she added.
"There seemed to be a catalogue of concerns."
Ms Gilbert added that she was "concerned" that other councils could be hiding behind similar false data.
She said she would be writing to every local authority in England to ensure all the information they held was accurate.
Inspectors sent to Haringey after the trial identified a string of "serious concerns" about the area's "inadequate" child-protection services.
They condemned everything from poor record-keeping to a failure to identify children at immediate risk of harm.