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 reported.
The practice is linked to a subculture where men become “nullos” - short for genital nullification, by having their penis and testicles removed.
A Met spokesperson said: “Between Tuesday 7 December and Friday 10 December 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.
Speaking of the flat raid, a neighbour told The Sun: “It was all very bizarre, there were police outside the flat for a few days.
“They were putting everything in plastic bags - it looked like computers and laptops.”
Mao Sugiyama, a Japanese artist, is the most renowned nullo after he reportedly had his genitals removed, cooked and served to paying guests at a dinner.
Sugiyama, who is asexual, had the procedure done voluntarily in Tokyo.
It is claimed he seasoned his genitals with salt and pepper, adding a garnish of mushrooms and parsley, before serving them to guests who had paid £160 each.