London mayor Ken Livingstone has blamed an insider at City Hall for breaking into the computer system and downloading intimate emails sent by his former race adviser.

Lee Jasper stepped down as Livingstone's aide on Tuesday night, claiming he was the victim of a racist media campaign after details of intimate emails from him to charity worker Karen Chouhan were published.

Scotland Yard today confirmed that it had launched an investigation into the alleged mis-use of computer data.

In an interview with LBC radio on Thursday, Mr Livingstone claimed the leaked emails were down to someone breaking into his office and hacking into Mr Jasper's computer.

"The emails weren't leaked. Somebody broke into the City Hall office and downloaded everything," he told host Nick Ferrari.

Responding to Mr Livingstone's explanation, rival Brian Paddick said: "If, as it appears, this was an inside job, there is clearly a growing mutiny at City Hall. It's time for someone with capable leadership and a proven track record to clean up City Hall."

Prime minister Gordon Brown has waded into the current uproar at City Hall, insisting that police should investigate the allegations facing Mr Jasper over misused public funds.

Mr Brown called for a thorough inquiry after Conservative leader David Cameron said the alleged activities by Lee Jasper were "completely unnacceptable".

At the same time, the London Assembly vowed to press on in its investigation into accusations made against Mr Jasper over the misuse of public money.

"This assembly will not be deflected from continuing to investigate whether London taxpayers' money has been properly and effectively spent, chair of the London Assembly, Sally Hamwee, said.