The Coalition government's moves to cut 15,000 public service jobs has coincided with a doubling in spending on private consultants with specialist skills, with the big four consultancy firms winning billions in work since 2012-13.

A new report from the Australian National Audit Office showed federal government consultancy contracts established because of "need for specialised or professional skills" grew from more than $200 million in 2012-13 to more than $500 million last financial year.

The big four firms have led a new report on government spending. Credit:Ryan Stuart

Job cuts since the 2013 federal election have seen the public sector workforce at the lowest level in nearly a decade and nearly $700 million being spent on consultancy contracts in 2016-17.

The figures include contracts which required independent research or assessment to be completed, and skills considered "currently unavailable" within the contract's home department or agency.