Mr Guy dined at the Lobster Cave restaurant with Tony Madafferi, a wealthy market gardener and the owner of the La Porchetta pizza chain, even though Mr Madafferi has repeatedly been accused by police in court of being a high-ranking member of Melbourne's Mafia.

In an affidavit filed in court in June to support Mr Madafferi's ban from Crown Casino and all Victorian racetracks, Detective Superintendent Peter Brigham said the police hold "substantial intelligence" indicating that Mr Madafferi had "substantial and close involvement with serious criminal conduct including drug importation, murder and extortion".

Mr Brigham also alleged that Mr Madafferi was "a known associate of prominent criminal entities and persons who have a history of significant criminal conduct that includes money laundering and drug trafficking".

Mr Guy has cultivated a "tough on crime" persona as Opposition Leader, but has previously been warned about associating with alleged Mafia figures after he claimed as planning minister he had "unwittingly" become the star attraction at a 2013 fundraiser hosted by Mr Madafferi at his Docklands venue centre.

A spokesman for Mr Guy acknowledged that Mr Guy had been at the dinner, but said it had been "hosted and organised by Liberal Party member and Executive Member of AUSVEG Victoria, Frank Lamattina", and was "held in open view at a popular restaurant".

The spokesman said the dinner had included "around 20 of his [Mr Lamattina's] relatives". However, asked if 25 people had been at the dinner, one of the attendees, nursery owner Bruno Diaco, a relative by marriage of Mr Madafferi, replied, "it wasn't anywhere near [that number]".

Fairfax Media has been told by another source that only seven were at the table, including Mr Guy and two other Liberal Party identities. The remaining four diners were Mr Madafferi and three of his relatives. Mr Lamattina is his cousin.

Mr Guy's spokesman said the Opposition Leader "did not organise the guest list and was not aware who Mr Lamattina's relatives are ... No political donations from anyone at the table has been sought or received".

However, sources with direct knowledge of the dinner have confirmed that Mr Guy's office was informed that Mr Madafferi would be one of the guests.

Mr Lamattina had settled the bill, the spokesman said, "of which Mr Guy's food and drink would have been well below the threshold for disclosure".

A joint Fairfax Media-Four Corners investigation has confirmed Liberal party official and fundraiser Barrie Macmillan met Mr Guy outside the Lobster Cave so no one would see the Opposition Leader entering or leaving with the other guests.

Mr Macmillan has played a key role in several Liberal Party local campaigns and has worked as an adviser to the federal Member for Dunkley, Chris Crewther. Mr Crewther said Mr Macmillan had worked as a casual adviser until January but had not worked for him since then.

Also at the dinner was Hawthorn footballer turned Liberal councillor Geoff Ablett, and two other Calabrian community members, Bruno Diaco, a relative of Mr Madafferi, and Vince Doria, a business partner of Mr Madafferi who co-owns the Docklands venue used for the 2013 fundraiser.

Mr Diaco confirmed he was at the dinner and said it had been organised by Mr Lamattina as a "private affair". There had been no talk of donations, he said.

Mr Lamattina angrily declined to answer questions, stating: "You print a lot of f---ing lies. If you want to see me you come and see me on the farm."

Mr Macmillan did not respond to multiple requests for comment.

It is understood Mr Macmillan organised the event with Mr Lamattina because Mr Madafferi and his relatives are long-time Liberal donors, and because Mr Lamattina had, at an earlier fundraiser, been promised a private dinner by Mr Guy.

Mr Guy's spokesman said: "The whole purpose of attending this gathering was to discuss public policy issues in relation to the vegetable growing industry with some of the biggest users of the market. Whatever their backgrounds are is not Mr Guy's concern, it's their use of a state facility ... and any cost of living impacts on consumers."

It is understood the diners discussed the move of the Victorian Fruit and Vegetable wholesale market from Footscray to Epping. Traditionally, Mr Madafferi and other greengrocers exercised significant influence at the Footscray market.

The Liberal Party is cash strapped, with some of its traditional wealthy donors withholding funds after a spat between party officials and long-time donors.

Even though the election is more than a year away, Mr Guy has already started appearing in tough-on-crime roadside billboards that say: "Safer Communities. Protecting Your Future."

A series of Fairfax Media and Four Corners reports over the past two years have shown that Tony Madafferi and Mr Lamattina were involved in a 2006 donations scandal in which the planned deportation of Mr Madafferi's brother, Francesco, a Mafia boss, was overturned after a long campaign of lobbying and donating to federal Liberal politicians. Francesco, a violent criminal and drug trafficker, was later jailed in connection to Australia's biggest ecstasy importation.

For three decades, policing agencies have alleged Mr Madafferi holds a senior rank in Australia's secretive Calabrian Mafia organisation.

The Australian Federal Police covertly filmed Mr Madafferi in a city park and at Crown Casino with several notorious Mafia drug traffickers in 2008 as part of a probe into Australia's biggest ecstasy importation.

Mr Madafferi, who also owns the national pizza chain La Porchetta, has never been charged with any crime and denies any wrongdoing.

In the early 2000s, police intelligence linking Tony Madafferi to allegations of "murder, gunshot wounding and arson" was detailed in court but vehemently denied by Mr Madafferi.

Prior to that, he was named as a suspected hitman in two coronial inquests in the 1990s. He was identified in a recent police intelligence briefing as the leader of a Calabrian Mafia cell in Melbourne that remains a powerful presence at Victoria's wholesale fruit and vegetable market.

Federal Police superintendent Matt Warren has alleged that Mr Madafferi has a "strong association" with major drug traffickers.

"We see him [Tony Madafferi] as potentially someone who associates and has close associations with established organised crime figures," Mr Warren previously told Fairfax Media and Four Corners.

In 2015, former NSW police assistant commissioner Clive Small, a Mafia expert, warned politicians to avoid political donors such as Tony Madafferi.

"I find that so extremely difficult to understand: how they could do it or how they could be so na??ve [in dealing with Mr Madafferi after media exposes]," Mr Small said.

After the Lygon Street murder of Mr Madafferi's lawyer and associate, Joe Acquaro, in 2015, Mr Madafferi's solicitor, Paulo Tatti, revealed in an affidavit filed in court that detectives had falsely accused Mr Madafferi of placing a $200,000 contract on Mr Acquaro's life. There is no suggestion Mr Madafferi was involved in Mr Acquaro's unsolved murder.

Mr Madafferi gained further notoriety after a 2015 Fairfax Media and Four Corners expose about his political donation activity. The expose detailed Mr Guy's appearance at the Madafferi political fundraiser in Docklands in 2013.

Mr Guy was planning minister at the time and his office claimed he had no role in Mr Madafferi's presence at the fundraiser. After the 2015 reports, Liberal politicians allegedly cut contact with Mr Madafferi.

Mr Madafferi was banned from Crown Casino that year by the Victoria Police chief commissioner amid extensive publicity, and after detectives investigated the Calabria-born businessman's extensive organised crime links.

Mr Madafferi is challenging that order in the Supreme Court, and the hearing is listed for August 14. Detective Brigham's affidavit in that case stated that: "[Mr Madafferi poses] ... a risk to the integrity of both racing and casino venues in Victoria."

The Howard government gave Mr Madafferi's brother, drug trafficker Francesco, a visa in 2006 after Tony Madafferi and Frank Lamattina lobbied and donated to several Liberal MPs.

The visa case was the subject of a national scandal, and sparked a federal police investigation into whether any politicians had been improperly swayed. By 2016, most senior Liberal MPs had cut contact with Tony Madafferi and some of his relatives who been involved in the lobbying campaign.

The federal police closed their donations-for-visa probe after finding insufficient evidence that any criminal offence had been committed. But police warned in a confidential report obtained under freedom of information that Australia's donations system was exposed to corruption.

In 2015, then senior Liberal minister Bruce Billson claimed he'd been "deceived" into assisting with the visa request. He described the lobbying campaign - which involved claims that Francesco was too mentally unwell to be deported - as a "contrived veneer covering a far darker and disturbing situation".

"As soon as I became aware of further information [and] criminal allegations ??? I ceased contact with all parties involved and stridently expressed my bitter disappointment to the individual family member who had first raised this matter with me."

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