A government watchdog has exposed some of the techniques federal public servants use to wrongfully prevent citizens from accessing their own records.

The Information Commissioner's investigation of the bureaucracy's biggest workplace, the Department of Human Services, revealed an organisation obsessed with process, that preferred legalese to plain English and had increasingly lost sight of its duty to share information.

In one Kafkaesque case, freedom of information officers told a man that recordings of his own voice breached his ex-partner's privacy because he had mentioned her.

Rather than give him the readily available recordings of his phone calls to the Child Support Agency, the FOI team proposed spending weeks of staff time going through each call and censoring the moments he spoke about his ex-partner.

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Another FOI applicant had asked for a copy of an "actual conversation" he had with department staff. The department refused his request, saying it had no audio recording of the phone call. But it did not tell him it had a written record of it.

The report also cited an applicant who wanted details of a call an official had made to another organisation, within a specific date range, that "apparently infers that I was attempting to extort money". The department denied that request, too, saying there was no document that mentioned "extortion", even though it had a similar record that matched the request.

The commissioner, Professor John McMillan, began investigating the department, which includes Centrelink and Medicare, after noticing a huge increase in the number of times it invoked its "practical refusal" power.

Under FOI law, government agencies can knock back requests for documents if processing them would "unreasonably" waste time and resources.

However, the department used this power 777 times last financial year, a more than twentyfold increase from two years earlier.

Professor McMillan said he had also received many complaints about a change in the department's culture.

The Welfare Rights and Advocacy Service, which uses FOI to help people gain access to benefits they were wrongfully denied, complained it had struggled to understand some of the department's letters since April last year.

"There has been a marked increase in length, complexity of language and use of what appears to be chunks of text that have been 'cut and pasted' and at the same time there has been a marked reduction in the number of documents released to a client," the service said.

Another organisation, the NSW Welfare Rights Centre, said FOI was the "only independent check" on the department, which sometimes failed to disclose all relevant records during legal hearings over disputed debts.

Professor McMillan, whose office may be abolished early next year, said the department was in the difficult position of receiving more than 100,000 requests for documents each year, but a less secretive culture would help it operate more efficiently.

"The default position in many government, or any other, organisations is to control information. Saying 'no' often seems the easiest answer – but that's not necessarily the case," he told Fairfax Media.

He said he understood why agencies turned to lawyers to deal with FOI and said their input was important.

But he cited the example of the Defence Department, which had greatly improved its efficiency in handling FOI requests in recent years.

"Their breakthrough came from taking FOI out of the hands of lawyers," Professor McMillan said.

"Treating everything as an analysis of legal principles is not always helpful. The simplest, most cost-effective way to administer access requests, whether under the FOI Act or otherwise, is to find out what will satisfy the applicant and do what you can to help them."

The Department of Human Services said it would begin to implement Professor McMillan's recommendations.

Its secretary, Kathryn Campbell, said it was "focused on improving the customer experience, particularly for our vulnerable and special needs customers".