BBC confirms 'data protection breach'
The BBC has said it is "urgently investigating" a breach of data protection by a former TV researcher.
The researcher, employed by an independent production company, spent four days working on Monday's Panorama.
The show found that Lutfur Rahman, Tower Hamlets' mayor, had increased funding to some Bengali-run charities. Opponents accused him of attempting to influence votes, which he denies.
The BBC said the breach involved material from confidential sources.
A spokesperson for the corporation said: "We can confirm that there has been a breach of data protection at an independent production company working with the BBC on a Panorama investigation as a result of unauthorised disclosure by a former researcher on the production team, in breach of her obligation of confidentiality.
"This breach includes material relating to the programme's confidential sources. Our primary concern is to protect our sources and we are urgently investigating the matter. We have also notified the Information Commissioner's Office."
In 2010, residents of Tower Hamlets voted in Mr Rahman as Britain's first directly elected Asian mayor.
Mr Rahman won as an independent with only 13% of registered voters.
Almost two-thirds of those who turned out to vote that day were from his own Bangladeshi community.
Opposition councillors say they believe the grants were made in return for electoral support.
Mr Rahman categorically denies the accusation.