New figures show the state government spends $150 million a year on consultants, or more than the budget for many government departments, leading to allegations its reliance on external advice is "privatisation by stealth".

As the government prepares to deliver a budget this week that includes cuts to department budgets, analysis of documents filed in Parliament shows it has been spending an average of $3 million a week on external consultants for the past two years.

Much of the advice behind the council merger process remains secret.

That amount exceeds the total yearly budget of several government departments, including State Emergency Services and the Office of the Director of Public Prosecutions, which have annual budgets of less than $130 million.

In its final year in office, the previous Labor government spent little less than two-thirds as much on management consultants, or just over $95 million unadjusted for inflation.