Liberal MP Cyril Smith wrote to the BBC in 1976 criticising its investigations into the "private lives of certain MPs".
The politician, who died in 2010 and has been accused of abusing children, expressed "deep concern" about a probe into an alleged South African campaign to discredit members of parliament.
According to letters in the National Archives, Smith told director general Sir Charles Curran: "I have reason to believe that you are employing a team (maybe two) to investigate the private lives of certain prominent MPs.
"So far as I am aware I am not one of them, and hence I write without personal involvement."
Smith said: "You are asking, I understand, for increased licence fees, and I think some of us, certainly me, would like to be assured that your expenditure is careful, wise and useful."
In another letter, Smith urged the then Home Secretary, Merlyn Rees, to ensure the BBC was not using public money for "muck-raking".
Former children's minister Tim Loughton told the BBC the former Rochdale MP's letters were "bully-boy tactics".
"It was an abuse of position that somebody as an MP was saying, 'You shouldn't look at us, we're above the law,'" he said.