The Serious Fraud Office (SFO) dealt with more than 200 inquiries and more than 100 cases in the year to June and needs more staff to deal with the work, the agency says in its annual report, released today.

"For an agency which has had fewer than 30 operational staff for most of the year, this is an impressive workload," chief executive Adam Feeley said.

"Ultimately, though, it is not a workload which is sustainable - there is inevitably a correlation between staff numbers, case numbers and timeframes."

He said that that in the past the SFO managed a high number of investigations and prosecutions but that resulted in there being four to five years between the start of an investigation and the conclusion of a prosecution.

Last year it tried to conclude as many cases as possible and reduce the number of active cases from 69 to 47.

"Notwithstanding the reduction of caseload, the ratio of staff to cases remains problematic," Feeley said.