South Tyneside Council says Twitter has released information after it acted in a US court to identify a Twitter user behind allegedly libellous statements.
The council went to court in California after three councillors and an official complained they were libelled in a blog called "Mr Monkey".
Council spokesman Paul Robinson said information had been disclosed by Twitter to its lawyers.
This was "being analysed by technical experts", he added.
'Five Twitter accounts'
Independent South Shields councillor Ahmed Khan is suspected by some of being the author of the blog, which has made a series of unfounded allegations against council leaders.
Mr Khan, who denies being the author, said he was first contacted by Twitter in April about a subpoena lodged with the Californian court.
He said he was told he had 21 days to lodge a legal argument against the action, otherwise the details would be released.
The councillor said he was told by Twitter that the information included IP identities, mobile phone numbers and e-mail addresses.
Mr Khan said the firm had also released 68 pages of other details, of which he said: "I can't decipher most of it."
He said he believed the council had been given the details of five Twitter accounts, two of which were his.
Mr Khan said: "I'm the kind of person who will tell you face-to-face what I think. I have no need to use an anonymous blog."
Mr Khan admitted being a critic of some council policies, but described the situation as "Orwellian".
He also also criticised the amount of money the council had spent on the case.
Mr Robinson denied press reports that the council's court action had cost "hundreds of thousands of pounds".
"We cannot confirm the cost of this legal action because it is ongoing, but it has so far cost less than £75,000," he said.
'Duty of care'
The Mr Monkey blog had made a number of accusations against the council's Labour leader Iain Malcolm, as well as David Potts, the former Conservative leader who now serves as an Independent councillor, Labour councillor Anne Walsh, and Rick O'Farrell, the council's head of enterprise and regeneration.
They are all named on papers delivered by the council's lawyers to the Superior Court of California.
Mr Potts said: "This is a deeply tawdry, perverted and seedy little blog that has been in existence for quite a while.
"It's no longer active, as I understand, but the information is still on the internet for all to see.
"This was a blog that didn't just affect councillors; it also affected council officers.
"We have a duty of care, as any employer does whether public or private, to defend not only our commercial interests, but also the interests of our employees.
"That's why we took the action, that's why we're pursuing it so aggressively, and I have no doubt that we will get there, and we will win.
"There have been many, many disgusting claims, which I won't repeat in order to protect my family and friends - allegations of corruption, sexual deviancy, of drug use."
A spokesman for South Tyneside Council said: "This legal action was initiated by the council's previous chief executive and has continued with the full support of the council's current chief executive.
"The council has a duty of care to protect its employees and as this blog contains damaging claims about council officers, legal action is being taken to identify those responsible."
He said he had no knowledge of councillors attending court hearings in the US.
A spokesman for Twitter said: "We cannot comment on any specific order or request.
"As noted in our law enforcement guidelines, it is our policy to notify our users before disclosure of account information."
Media law experts suggest the case may prompt more UK citizens to take action in the US, where Twitter is based.
Lawyers challenged Twitter in the High Court in London to reveal the identities of its users who violated a super-injunction involving Manchester United footballer Ryan Giggs.
MP John Hemming named the star in Parliament as the footballer who had used a super-injunction to hide an alleged affair, after Mr Giggs's name had been widely aired on Twitter.
Media lawyer Mark Stephens, who represented Wikileaks founder Julian Assange, said: "I am unaware of any other occasion where somebody from this country has actually gone to America and launched proceedings in a Californian court to force Twitter to release the identities of individuals.
"The implications are that people who have had their name released can actually now go to California and begin proceedings.
"Local authorities cannot sue for libel and, if individual councillors have been defamed, they should take proceedings at their own cost."