A Westminster councillor who helped trigger the inquiry into the "homes for votes" scandal is due before an adjudication panel.
Dame Shirley Porter was the daughter of the Tesco founder
Paul Dimoldenberg is accused of leaking confidential documents about disgraced former leader Dame Shirley Porter.
The Labour councillor faces charges of bringing the council into disrepute.
But says he acted in the public interest in giving the documents to the BBC and hastened the pursuit of millions in fines owed by Dame Shirley.
In 2003, Mr Dimoldenberg sent e-mails to a BBC Radio 4 Today programme reporter disclosing confidential information from the council.
Paul Dimoldenberg could be disqualified from office
This was used in reports suggesting the council was not doing enough to recover the £42m owed by its former leader Dame Shirley Porter.
She, along with her deputy, had been surcharged for what the district auditor had called disgraceful and improper conduct - selling off council homes in marginal wards to boost the Conservative vote.
The council argues that by disclosing information given him in confidence - some of it subject to court gagging orders - Mr Dimoldenberg was in breach of the councillors code of conduct and brought his office into disrepute.
He says disclosure was in the public interest - and that after the Today reports the council intensified efforts to recover the money, leading to a £12m settlement from Dame Shirley last year.
The panel will sit for three days. if it finds against the councillor he could be suspended or disqualified from office.