No "secret deal" exists between the Victorian Government and the state's firefighters' union, the Deputy Premier says, despite the union's threat to release the details of confidential promises as it attacks the appointment of a new fire chief.

Key points: UFU will not confirm if recording of discussion between the Government and union exists

UFU will not confirm if recording of discussion between the Government and union exists Union criticises appointment of former UK fire chief to MFB's top job

Union criticises appointment of former UK fire chief to MFB's top job State Government says no secret deal made

The United Firefighters Union has reacted angrily to the news that Dan Stephens — the chief of England's Merseyside Fire and Rescue Service — will head up the Metropolitan Fire Brigade (MFB).

United Firefighters Union (UFU) secretary Peter Marshall told ABC Radio Melbourne that "promises" had been made by Victorian Premier Daniel Andrews, and "the truth would come out", but he would not elaborate on what the alleged assurances were.

New MFB chief Dan Stephens worked for Merseyside Fire and Rescue Service in Liverpool. ( Merseyside Fire and Rescue Service )

Mr Merlino, who is also the Emergency Services Minister, said no such deal existed and he was not concerned about Mr Marshall's claims.

"No there wasn't. The promise we made was to deliver 450 career firefighters to the CFA (Country Fire Authority) and MFB and that's exactly what we've done," he said.

There has long been talk in state political circles about the possible existence of a secret recording that the union has of Mr Andrews.

Mr Marshall yesterday would not confirm if there was a recording of any discussions between the Government and the union.

Asked if there were audio recordings, Mr Merlino said "no".

During the interview, Mr Marshall was critical of the appointment of former UK fire chief Dan Stephens to lead the MFB, saying it was a "bad call".

Mr Merlino said the appointment of Mr Stephens was based on the unanimous recommendation of a selection panel.

"What I've been focused on … is reforming our fire services and improving community safety," he said.

"We've had decades of conflict between management and the workforce in our fire services. It's always been a difficult area to reform.

"We've always been determined to find the best possible candidate and a key part of [Mr Stephens'] role will be to rebuild the relationship between management and workforce."

The fractious relationship between the UFU and the state's Labor Government has been a major challenge for Premier Daniel Andrews, who has been frequently accused of backing the union in its industrial battles with fire brigade management.

The relationship between MFB staff and management has been fractious. ( Supplied: Steve Moore )

In 2016, Jane Garrett quit cabinet over a proposed workplace deal for union firefighters, which was resisted by management but backed by the Premier

Opposition Leader Matthew Guy said the Government should be clear with voters about what agreements were made with the union before the last election.

"They've been held to ransom by this union for the best part of three years," Mr Guy told ABC Radio Melbourne.

"Victorians need to know what is in the deal the Government has with the UFU."

MFB president Jasmine Doak said Mr Stephens was "absolutely the best candidate" to lead the fire service.

He is due to start at the end of May.