A whistleblower who leaked documents about the Westminster 'homes-for-votes' scandal did not bring the council into disrepute, a panel has ruled.
Paul Dimoldenberg is Labour group leader at Westminster Council
Paul Dimoldenberg gave the BBC secret papers about the council's disgraced ex-leader Dame Shirley Porter, who owed the council millions in surcharges.
He said he acted in the public interest and added justice had now been done.
A watchdog said he had breached the code of conduct but had gained neither financially nor politically.
In the 1990s Dame Shirley, the Conservative leader of the council, was found guilty of "disgraceful and improper gerrymandering" by the district auditor.
She and her deputy had deliberately kept council properties empty in marginal wards because tenants were thought less likely to vote Conservative than owner-occupiers.
She was ordered to pay £27m in compensation, but the Tory-controlled council was slow to collect, according to Mr Dimoldenberg.
The Adjudication Panel for England found Mr Dimoldenberg, who was leader of the Labour group on the council, had committed a technical breach of conduct rules in releasing secret High Court documents to BBC Radio 4 Today journalist Andrew Hosken.
He passed on the information in 2003 to try to publicise what he called the council's "deliberate" slowness in collecting £27m demanded in compensation from Dame Shirley, for her part in the housing scandal.
Mr Dimoldenberg, 55, said he was "delighted" with the panel's decision.
The local government watchdog could have banned him from public office for five years.
But panel chair Steve Wells told Mr Dimoldenberg: "No sanction should be imposed upon you.
"We noted in particular there was no financial gain or political kudos. Neither was there any damage caused to Westminster City Council in its recovery proceedings."
After the ruling the councillor said: "This is great news for councillors in a democracy. It means that you can no longer hide behind documents being labelled as confidential.
Westminster Council defended its decision to take the case, saying councillors could take such concerns to the district auditor, audit commission or city solicitors.
"But councillor Dimoldenberg didn't do all of these things, he chose to go to the media straight away," said spokesman Kit Malthouse.
Dame Shirley now lives in Israel
Dame Shirley, who now lives in Israel, had made a sworn statement in 2002 claiming to have just £300,000 in assets even though her fortune is estimated at £70m.
She eventually agreed to a £12.3m settlement in April 2004 which, the councillor's defence lawyer argued, was a direct result of Mr Dimoldenberg's actions.
Gavin Millar QC said he was a whistleblower whose rights as a journalist's source were protected under the Human Rights Act.
But Anthony White QC, for the panel's ethical standards officer, pointed out that by 2003 the council had launched a series of High Court actions aimed at recovery.