Seven men were arrested after reports of castration procedures being broadcast live online.
They were held in Finsbury Park, north London, in December, when Metropolitan Police officers spent four days searching a home in the area.
Amputations were allegedly carried out in a basement flat and broadcast on a pay-per-view channel that was promoted via a Twitter account, The Sun newspaper reported.
The practise is linked to a subculture where men become “nullos”, short for genital nullification.
A Metropolitan Police spokesman said: “Between Tuesday December 7 and Friday December 10 2021, officers from the Met’s Central Specialist Crime command conducted a search warrant at a residential address in the Finsbury Park area in connection with an investigation into an allegation of grievous bodily harm.
“A man, aged in his 40s, was arrested in relation to this investigation and is currently on bail. Six other suspects were also arrested and released on bail in connection with this matter.”
The other suspects are aged in their 30s, 40s, 50s and 60s.