The 50-year-old tourist is said to have been attacked in the holiday resort of Sorrento in October 2016.
She was allegedly given a date-rape drug in a drink she accepted from two barmen on the last night of her holiday, according to the Daily Telegraph.
She was then taken to a hotel room and raped by the two men before being assaulted by at least three other men, who raped her in a different room, the newspaper reported.
The woman contacted police in Kent on her return to the UK and DNA testing was ordered.
Prosecutor Alessandro Pennasilico said the investigation was aided by the DNA testing.
Investigators also got a breakthrough when the woman recalled a tattoo that one of her alleged attackers had on his neck, Italian news agency ANSA reported.
It was unclear what caused the delay between the sexual assault being reported to police and the arrest warrants being issued.
Mobile phones of male employees at the hotel were seized and the suspects were allegedly found to have chatted about the attack and exchanged photos taken of the woman while she was being raped.