A government department should not be used by Victorian Labor to cost its election policies to defuse public sector independency concerns, a new report says.

In a report tabled on Tuesday, Victoria's Parliamentary Budget Office recommended it be the sole provider of election costing services to all political parties.

The Andrews Labor government set up the independent agency before the 2018 election to provide the opposition and minor parties with a mechanism to cost their policies.

But it has continued to rely on the Department of Treasury and Finance to run the numbers on its financial-related election pledges, including for last year's state poll.

The parallel service comes at the expense of operating a single entity that costs policies on a comparable basis for voters and raises questions about the public sector being seen to be apolitical during caretaker period, the PBO said.

"Clearly there is a longstanding and well-documented perception that the Department of Treasury and Finance election costing service isn't independent, that has been left unaddressed for some time," the report said.

"Put simply, it is not possible for the public sector 'to protect its reputation and ensure that it remains trusted by the incoming government' and continue to offer a parallel election costing service during an election period."

While not directly calling into question the independence of the public sector during caretaker period, the PBO said it is seen to be by political parties that may form government.

The Andrews Labor government does not support legislative reform to enshrine the PBO as the sole election costings provider, the PBO said.

However, it recommends the Department of Premier and Cabinet review caretaker conventions to assess the impact of offering a parallel service against the principle of maintaining an apolitical public sector.

The agency is also seeking greater financial independence from government, a link to the budget process and improved transparency on budget contingencies.

Shadow Treasurer Brad Rowswell said a strong PBO is critical to ensuring taxpayers' money is spent responsibly.

"Only Daniel Andrews would set up an independent agency to cost policies, and then refuse to use it," he said.

The PBO prepared 1768 costing responses for the 2022 state election, up 69 per cent from four years ago.

In all, 842 election commitments were made across five political parties, with 58 per cent of those featuring a funding announcement.

The Victorian government has been contacted for comment.