The arrests are part of a two-year investigation, codenamed Operation Vaulter, and follows the arrests of 17 people in north-west England last September.
In total, four men and one woman were arrested in Forfar, in Angus, and one woman was arrested in Turriff, Aberdeenshire. Four sites were searched.
HMRC director of operations for criminal investigations Chris Harrison said: “The sophistication of the organised crime gangs behind these frauds means our investigations are increasingly complex.
“However, we are committed to bringing the criminals responsible to justice and to recovering the money stolen from the British taxpayer, wherever in the world our investigations lead.
“This is not victimless crime, but organised crime that causes real harm.”