The ombudsman has criticised the construction industry investigator's office for breaching confidentiality of people it is examining and using questionable interviewing methods.

Fair Work Building and Construction, headed by director Nigel Hadgkiss, is the federal office in charge of investigating breaches of building laws and codes as well as workplace laws where they relate to the construction industry.

Commonwealth ombudsman Colin Neave looked at 12 examinations by Fair Work Building and Construction in the 2014/15 financial year and made a number of recommendations to the watchdog’s director in a report tabled in federal parliament.

In several interviews, the ombudsman found FWBC examiners “completed the examinee’s sentences rather than allowing the examinee to finish”, asked examinees to speculate on matters or used questions to suggest evidence.

In one case, the ombudsman found investigating officers breached the confidentiality of three people by serving all three examination notices at the same place and the same time.

While Mr Hadgkiss did not consider the process to be unfair, the ombudsman said it “did appear to breach the confidentiality of the examinees” and notices should always be served separately whether or not the examinees are known to each other.

The ombudsman also found in eight of the 12 cases Mr Hadgkiss had stated a preference to the examinees that matters regarding the examinations not be discussed with others.

“Whilst the FWBC must keep the information obtained under an examination notice confidential, under the FWBI Act, the director is precluded from requiring the examinee to make undertakings of confidentiality,” the report said.

Mr Hadgkiss said in response that he believed as long as a request not to disclose information is balanced by a clear statement that there is no ban on information disclosure “it seemed reasonable that an examinee be asked to respect the nature of the investigative process on foot and thereby be invited to exercise their own discretion”.

Delays in examination times were also criticised, with the ombudsman suggesting the office consider limiting its work to two examinations a day.

Mr Hadgkiss said he was reluctant to set any limits because of cost implications and inefficiencies.

The ombudsman also asked the director to take a fresh look at the way legal expenses are covered.

The Turnbull government is seeking to replace the FWBC – which industry figures consider to be a “watered-down” agency – with the Australian Building and Construction Commission.