The NSW government spends twice as much to use consultants instead of existing staff, according to a report that also found about 20 per cent of the almost $1 billion in spending on consultants in the five years to 2022 was on work that did not require specialist skills.

However, a NSW government report into the use of consultants and contractors by the state, published last week, also acknowledged that using external advisers had the advantage of avoiding costs associated with bringing on additional public servants.