Ben Carroll has been Victoria’s premier for less than 24 hours, and he already faces a decision that will define his leadership.

Does Carroll have the courage to establish a royal commission into criminality and corruption on the Big Build that not only goes after low-hanging fruit, like the infantile and abusive former CFMEU boss John Setka, but also seeks to hold politicians like Jacinta Allan accountable for the wrongdoing that occurred on their watch?

Or will it be a Claytons inquiry that perpetuates accusations of a long-running cover-up that dogged his predecessor, Allan?

A royal commissioner should have the authority to ask why Allan resisted a searching, independent inquiry into wrongdoing by the CFMEU and its gangster mates on major Victorian projects. The commission must be allowed to ask, on behalf of Victorians, whether her actions – or inaction – contributed to an environment that allowed wanton misbehaviour to take root.

Allan was the minister responsible for the Big Build when the union, alongside its bikie and underworld backers, moved in, and got rich or powerful, or sometimes both.

She was in charge, either as minister or premier, as the Labor government enabled the CFMEU’s Big Build power grab over road, hospital and rail projects.

A royal commissioner should determine whether Allan did so wilfully or recklessly. But the fact it happened on her watch is indisputable.

Was it for reasons of factional convenience and political stability that Allan’s office allegedly pressured major contractors to allow the CFMEU to take over the Gap Road level crossing project in 2022, bringing with it a labour hire firm whose boss recently pleaded guilty to falsifying documents involving suspected bribes?

Was the Metro Tunnel consortium spot on when, in a dynamite 89-page document dated May 2024, it accused the Labor government of forcing it to cede control to the CFMEU on parts of the taxpayer-funded mega-project – including which subcontractors could be used – leading to a $200 million blowout in labour hire costs?

Was famed corruption buster Geoffrey Watson right in estimating the cost of avoidable wrongdoing and rorts on the Big Build at $15 billion? Or is it closer to $1 billion? And, given it’s men like underworld figure Mick Gatto who profited from this scandal, does it really matter if it’s $1 billion or $15 billion? It’s still a bloody big number.

In mid-2023, while Allan was minister, did her office deliberately refuse to sign off on explosive secret briefings sent to it by senior public servants who sought to warn her – unsuccessfully it turns out – to act on the growing CFMEU cancer? This was a full year before it became public in the media.

And if they did so, was the intention of Allan or her staff to ensure plausible political deniability?

Even without a royal commission, one thing is certain. Allan’s two-year refusal to ensure the full answering of these vital public interest questions and plenty of others has had the effect of cover-up, deliberate or not.

Victoria now awaits to see if Carroll grasps this rare opportunity for true accountability and launches a royal commission with expansive terms of reference and appropriate powers.

To achieve this, he must appoint an independent and apolitical royal commissioner (or commissioners) with the ability to tap phones, access state and federal police intelligence and hold private and public coercive hearings. It must be backed by a fearless team of police investigators, analysts and lawyers.

Victoria needs a true corruption buster who replicates Queensland royal commissioner Tony Fitzgerald, not an arch-conservative union-bashing jurist or a Labor-aligned, union-friendly former judge.

The royal commission must not only investigate how honest workers were sold out by rotten CFMEU bosses, led by the Gatto-loving Setka and his allegedly crooked deputies Derek Christopher (who allegedly received free home renovations from building companies), Elias Spernovasilis (who used his union power to place his criminal bikie-linked relatives and mates onto Big Build projects), John Perkovic (who allegedly copped up to $3 million worth of bribes from bosses, including those exploiting union members), and Joe Myles (who allegedly built an army of bikie-linked union muscle on taxpayer projects and pressed the financial interests of Big Build firms run by criminals and domestic violence perpetrators).

It is crucial this commission also probes Victoria’s underworld. Gangland figures such as Gatto and his mate John Khoury, along with bikies who made the Big Build their playground, warrant ferocious attention.

The federal police from Operation Rye and state police from Taskforce Hawk, who have already been investigating allegations about the pair’s involvement in this scandal, can be seconded into the royal commission, bringing much-needed investigative experience.

At the same time, federal and state police, along with WorkSafe and other regulators, will also need to be held to account for not acting until the media blew up the scandal in July 2024.

And where the hell has IBAC, the state’s anti-corruption watchdog, been?

Building companies, including the large “tier one” firms that turned over billions of dollars in public funds, must be asked why they turned a blind eye to the employment of bikies or rotten subcontractors on major rail and road projects.

For too long, select big firms have blamed everyone but themselves.

More than anything, Carroll’s royal commission must exhaustively probe the political decision-making that enabled the CFMEU’s Big Build operation and overlapping corruption and wrongdoing that flowed from it.

It must grill both Allan and Daniel Andrews, and examine whether Victoria’s public servants acted without fear or favour overseeing the Big Build and reporting to ministers.

Carroll faces an immediate test of his courage and commitment to integrity. One of the ministers who helped roll Allan to crown Carroll is Luba Grigorovitch.

She was elected with the help of the CFMEU in 2022. She has pointedly refused to denounce Setka’s behaviour.

The union also pressured Big Build companies we now know are likely corrupt to donate to Grigorovitch’s election campaign and that of state Labor in 2022. The Age is not suggesting Grigorovitch knew this was happening.

This ALP money trail needs to be followed by the royal commission, wherever it leads and whatever it finds.

Will Carroll have the political guts to allow his royal commission to pursue answers that could put heat on members of his own cabinet?

If he doesn’t, you can assume Labor also won’t follow through on what are likely to be costly and complex recommendations the royal commissioner will make in about 18 months.

By that time, the opposition could be in power. The Coalition must also commit to an independent, apolitical and properly empowered royal commission if it wins power.

For now, it’s Carroll in the hot seat. Victorians are about to find out if their newest premier is, as he claims to be, truly different to the politician he replaced.

Building Bad: Explore our investigation

The original investigation: Explore the multipart investigation that plunged the construction industry into crisis.

Damning probe: Corruption buster Geoffrey Watson’s full report of his investigation into the CFMEU contained an extraordinarily damning exposé of corrupt and criminal behaviour.

The cost: ‘Extraordinary, unforeseeable’ and extremely costly: CFMEU price tag of each Metro station revealed.

Biggest projects affected: Eleven of the biggest infrastructure projects in Victoria – including the multibillion-dollar Suburban Rail Loop and North East Link – are the subject of 56 separate allegations of fraud, corruption, theft and criminal behaviour.

Administrator fights back: CFMEU’s new administrator has declared the culture in the union’s Victorian arm remains broken.

‘Grind it out’: Allan defends her royal commission refusal to cabinet.Should have called Saul: Economist’s verdict on inflation versus corruption.

Treatment of women: A company that secured huge contracts as the leading women-led supplier of female workers on Labor’s Big Build is owned by a male serial domestic violence abuser, was managed by a male drug trafficker also accused of family violence and has deep links to bikies and violent criminals.

Turmoil within the administration: The senior barrister appointed to clean up the corruption and crime-tainted CFMEU, Mark Irving, quit in a major challenge to the Albanese government’s attempts to reform the sector.

Warning to state: The Allan government’s infrastructure tsar privately warned the premier of serious wrongdoing on Labor’s $100 billion Big Build.