Jack Dromey, the Labour Party treasurer investigating secret loans to the party, has previously complained that "rich men are too influential at Downing Street".
The trade unionist has been seen as a New Labour-style moderniser
Treasurer since 2004, Mr Dromey has said he knew nothing about loans totalling millions of pounds made to the party in the run-up to the 2005 general election.
As treasurer he is a member of Labour's governing body, the National Executive Committee (NEC) - to whom he will give a preliminary report on the affair.
He is also calling on the Electoral Commission to investigate the issue of loans to political parties from non-commercial sources.
NEC members are also in the National Policy Forum, which oversees the development of party policy.
Mr Dromey, who is married to Constitutional Affairs Minister Harriet Harman, is also deputy general secretary of the Transport and General Workers' Union (TGWU).
The veteran trade unionist was elected to the post in October 2003.
In an election for the top job earlier that year, Mr Dromey was seen as a New Labour-style moderniser but lost to left-winger Tony Woodley.
Mr Dromey said in the campaign that "unreconstructed trade unionism" played into the hands of the Conservatives.
But he insisted he was "no pussycat" and accused the government of losing its way.
He also called for legislation to allow workers a say on executive salaries.
His trade union activities have seen him campaign for the rights of workers including defence staff and House of Commons cleaners.
The 57-year-old also campaigned for the setting up of the Gangmasters Licensing Authority watchdog after at least 21 cockle pickers drowned in Morecambe Bay in 2004.
Ms Harman and Mr Dromey have three children
In January this year, Mr Dromey called for public money to be made available to encourage people's involvement in politics.
"The time has come for greater public investment to help political parties engage with citizens, responding to their needs," he said.
Mr Dromey and Ms Harman have two sons and one daughter.