The arrests were made during early-morning raids in Lancashire, Tyne and Wear and Worcestershire.
Police said eight women suspected of being trafficked to the UK from Romania for prostitution were rescued during the raids in Blackburn, Preston, Blackpool, Gateshead and Evesham.
Police said it was one of the biggest operations of its kind in the country.
The detainees - seven men and one woman - are being questioned by detectives on suspicion of conspiring to traffic for sexual exploitation and conspiring to incite prostitution.
Those arrested were:
Det Insp Mark Vaughton of Lancashire Police said: "Today's arrests are the latest stage of a long-running proactive investigation into the activities of a Romanian organised crime group which we believe has been trafficking women into the country for the purposes of prostitution."
He added: "Modern slavery is not something confined to history, it is still happening today and it's happening in Lancashire."
Lancashire Police Crime and Commissioner Clive Grunshaw said: "These were highly-organised gangs making thousands of pounds, exploiting the most vulnerable women and girls."
Eight people were arrested as part of an investigation into a suspected human trafficking gang.