Childcare regulator Ofsted has admitted making a "serious and deeply regrettable error" in failing to disclose potential evidence during the high-profile Sharon Shoesmith High Court case related to the death of Baby P.
Late disclosure came in the wake of a Freedom of Information request.
Today a judge ordered that the case be reopened for further investigation.
This has wrecked the timetable for a decision on the legal bid by the former head of children's services at Haringey Council in east London to have her sacking following the Baby P tragedy declared unlawful.
Ms Shoesmith, 56, was dismissed from her £130,000-a-year post last December after a damning Ofsted report into her department's failings.
Ofsted's lead inspector, Heather Brown, described the quality of practice in the department as the "worst I had ever seen".
Mr Justice Foskett was due to give his judgment at the High Court in London on Friday this week.
But today he called a special hearing and announced in open court that new evidence had now come to light from Ofsted which must be examined to see if it was relevant to the case.
Ofsted apologised "unreservedly" in court for failing to disclose in good time the contents of an Ofsted inspector's notebook and various emails and early drafts of the devastating report last November on Ms Shoesmith's department.
In particular, the judge ordered Ofsted to give the court "a full explanation" of how it was that requests from Ms Shoesmith's lawyers for information about the existence of the draft reports "was dealt with in the way it was".
The judge said the request was made, then "batted away in one particular fashion at the beginning", then the reports were said not to exist - "and now they do".
The judge said: "I want chapter and verse on that."
He said the failure to disclose documents in good time meant his plans to give judgment this week must be put back, delaying his ruling until near Christmas, or possibly even later.
He ordered Ofsted to pay the legal costs of today's hearing on an indemnity basis - the highest level a judge can award - and said the regulator must meet the cost of Ms Shoesmith's lawyers going through the newly disclosed evidence to see whether or not it was relevant.