According to the PJ, the woman was detained for tax fraud, social security fraud and criminal association. She is to be brought before a public prosecutor at Lisbon's appeal court for preliminary questioning.

The detention, by the force's National Anti-Corruption Unit (UNCC), took place as part of an investigation dubbed 'Operation Octopus' in the wake of investigations carried out in Portugal and on the basis of a European arrest warrant issued by the authorities in Belgium.

As part of the investigation the PJ on Tuesday carried out searches of two premises in the Lisbon area.

In a statement, the PJ said that the investigation is focussing on “three Belgian transport companies that are believed to have used the services of a criminal organisation operating in Portugal and Slovakia [to] evade the laws on social security."

"These Belgian companies are suspected of having defrauded the Belgium social security in the amount of close to seven million euros," it said.

The PJ are working as part of an international team that includes French, Belgian and Slovak police. Also as part of the operation, Flemish police carried out searches of 12 premises in various parts of Belgium, the statement said, adding that two people were detained and a further five brought in for questioning as a result of the searches in other countries, while the Belgian authorities also seized 10 vehicles.