A 27-year-old British man was among six people arrested over an alleged £11 million plot to smuggle amphetamines from Britain into Australia.
The man, from Kidderminster, was held in Liverpool on Monday and has since been released on police bail pending further inquiries, West Mercia Police said.
The six were arrested on suspicion of money laundering and the importation of 8kg of amphetamine, believed to have a street value of at least £11m (20 million Australian dollars).
The other five, including alleged members of the Rebels Motorcycle Club in Australia, were detained in Queensland and Tasmania, West Mercia Police said.
They will appear before magistrates there on charges relating to the trafficking, possession and importation of a prohibited drug.
The Australian Crime Commission said the amphetamines were intercepted in three packages after being posted through an international parcel courier service.
Richard Grant, Australian Crime Commission national manager of investigations, said the syndicate was allegedly operating both domestically in Australia and internationally.
He said: "The investigation indicated the men were planning to import two packages of illicit drugs through an international parcel courier service.
"As a result, Tasmania Police and ACBPS officials intercepted two packages sent from the United Kingdom which contained approximately 4kg of amphetamines.
"Two further packages totalling another 4kg were later intercepted in Queensland."
West Mercia Police worked with the Australian Crime Commission, which coordinated the operation. It also involved Tasmania Police, Queensland Police Service, Australian Federal Police (AFP) and the Australian Customs and Border Protection Service (ACBPS).
Detective Inspector Carl Moore, from West Mercia Police, said: "This is another example of the international nature of many organised crime investigations; we work with policing agencies across the world.
"We have been keen to share our intelligence and expertise with our Australian counterparts to aid their inquiries and if it leads us to criminality taking place in the UK, all the better.
"We will now be working together to ensure our efforts lead to charges for those we believe have been involved in the criminal drugs trafficking operation."