Links between the Calabrian Mafia and senior Australian politicians have been uncovered in a joint investigation by Four Corners and Fairfax newspapers.

The year-long investigation found the Calabrian Mafia, known as 'Ndrangheta, had used a number of well-known party donors to put a "legitimate public face" on its activities.

The 'Ndrangheta is one of the world's most powerful criminal groups and is thought to be one of the major players in the world of international drug trafficking.

In Australia it operates using threats and violence in both legitimate businesses, such as fruit and vegetables, and illegitimate businesses, such as drugs.

The investigation has revealed a series of contacts between known and suspected criminals and senior politicians.

On one occasion, a man with deep mafia associations met then prime minister John Howard and other top Liberal Party figures at a fundraising event. It is not suggested that Mr Howard knew of the connection.

The investigation has also revealed donors have lobbied on behalf of a mafia figure to a host of Liberal and Labor MPs over issues related to their businesses.

Son of alleged mafia boss did work experience at embassy

Four Corners can reveal the son of another alleged mafia boss did work experience at the Australian embassy in Rome while former Liberal minister Amanda Vanstone was ambassador.

Prior to his placement, Italian authorities were sharing sensitive information about the alleged mafia boss through the embassy.

Ms Vanstone is at the centre of two cases uncovered during the investigation. ( AAP: Lukas Coch )

While there is no direct evidence the embassy placement — which involved the man's son working in a clerical role — led to any actual security breaches, security agencies have described it as a major lapse.

Ms Vanstone, who is now retired from politics, is also at the centre of another episode uncovered during the investigation.

When she was immigration minister in the Howard government, she granted a visa for a crime boss who was later jailed for drug trafficking and implicated in a murder plot.

The man, who is the brother of a well-known Melbourne businessman, has an extensive criminal history in Italy.

He was set to be deported, but his family used its money and influence to conduct a lobbying campaign with some of the country's most powerful Liberal politicians — including Ms Vanstone.

Eventually in 2005, the man was granted a visa to stay in Australia on humanitarian grounds.

There is no suggestion Ms Vanstone acted improperly in either case, though confidential police assessments suggest it indicates her South Australian Senate office had likely been infiltrated by mafia figures.

Just a couple of years later, the man was implicated in one of Australia's largest ever drug busts.

'Lack of checks' in donations system leading to 'loopholes'

Who are the 'Ndrangheta? A mafia group from Calabria in the south of Italy. There are thought to be roughly 6,000 members in the world today.

A mafia group from Calabria in the south of Italy. There are thought to be roughly 6,000 members in the world today. Whilst not as well-known as the Sicilian mafia, the 'Ndrangheta is the most powerful criminal organisation in the world.

Whilst not as well-known as the Sicilian mafia, the 'Ndrangheta is the most powerful criminal organisation in the world. The group earned the equivalent of around 3 per cent of Italy's gross domestic product in 2014, mostly from illegal drugs.

The group earned the equivalent of around 3 per cent of Italy's gross domestic product in 2014, mostly from illegal drugs. Instead of the pyramid structure of bosses used by other mafia groups, the 'Ndrangheta recruits members on the criterion of blood relationships and marriages.

Instead of the pyramid structure of bosses used by other mafia groups, the 'Ndrangheta recruits members on the criterion of blood relationships and marriages. The group's best-known crime was the 1973 kidnap of the grandson of oil tycoon John Paul Getty. His ear was chopped off to garner a ransom from his grandfather.

The group's best-known crime was the 1973 kidnap of the grandson of oil tycoon John Paul Getty. His ear was chopped off to garner a ransom from his grandfather. Known as "The Honoured Society" in Australia and reportedly involved in the Victoria Market murders in 1963.

The report also details how "loopholes" in the donations system, and the long-running failure to reform it, continue to expose Australian politicians to potential corruption.

Through Freedom of Information laws, the investigation obtained a 2009 AFP report that described a "lack of checks and oversight" in the Australian political donations system as "significant" failings.

"As it stands, political parties and candidates can receive significant support and financial contributions through avenues not covered by the statutory disclosure regime," the AFP report said.

"Loopholes" in the oversight system mean it is "difficult to identify any bribery in the form of political donations".

The report states the Australian Electoral Commission has attempted to address this on many occasions, but that many amendments have not been passed by the Federal Parliament.

The document was written after an investigation into the mafia's fundraising activities.

Watch Four Corners — The Mafia in Australia: Drugs, Murder and Politics on ABC iView.

Next week Four Corners will look at the inside story of the world's biggest ecstasy bust, the next crop of mafia leaders in Australia and one senior Mafioso's Labor connection.