The Complaints Commissioner has used his annual report to highlight problems his office faced when dealing with the Financial Services Authority (FSA).
Sir Anthony Holland said he had told the FSA board "on a number of occasions" that for complaints to be dealt with effectively the Complaints Commissioner's Office must have access to all documentation.
"The commissioner would also reiterate that when reviewing a complaint it is (initially) a matter for the complaints team and (later) for the commissioner rather than the relevant department within the FSA to decide upon what is relevant material which should be disclosed in connection with the complaint," the report said.
Holland said failing to provide full disclosure to the complaints team immediately suggested affected people had "acted inappropriately and are trying to ‘hide' their actions".
He added: "Such action is an unattractive position for the regulator or any body undertaking a public function to accept. The success of the complaints scheme to aid the regulator in carrying out its difficult, and often implied role, is to ensure that total transparency is always proffered to those charged with the investigations whether the investigation is internal or in the hands of the commissioner's office."
Since 1 April 2012, the Office of the Complaints Commissioner concluded 128 cases.
The report said individual consumers accounted for 80% of overall complainants compared to 78% of complainants last year, the remainder being made up of solicitors on behalf of their regulated clients, IFAs, third parties and individual firms.
Joined as head of strategy, multi asset, in June
Group income protection
Nine in 10 do not have income protection
Set to become part of Single Financial Guidance Body