Police said they had made the arrests on Sunday and Monday at addresses across England after becoming aware of a "potential serious threat" towards the religious event.
The event, attended by about 15,000 people, was held at a country house in Suffolk, eastern England, from July 9 to 12 and mostly went ahead as expected, apart from closing earlier than planned on Sunday.
Interior minister Shabana Mahmood said she knew the news would be concerning for Muslims in the United Kingdom.
"We must stand against hatred and we must unite around our shared belief in a country that is open, generous and tolerant to all our communities," she said in a post on X.
The UK raised its terrorism threat level to "severe" in April, signalling that a terrorist attack was considered highly likely, and counter-terrorism police head Helen Flanagan said the arrests on Monday were a "stark reminder" of that threat level.
Eight men remain in police custody having been detained under the Terrorism Act, the statement said, while three other men were arrested on suspicion of conspiracy to murder, and a woman was arrested on suspicion of assisting an offender.
Those arrested were aged between 27 and 60 years old. #
A number of addresses in London and the surrounding areas, and in eastern England and near Manchester are being searched.
