Eight men remain detained under terrorism powers as part of a wider investigation into an extreme right-wing terror threat.
The arrests relate to an extreme right-wing terror threat targeting the UK Ijtima event at Shrubland Estate in Suffolk.
Twelve people were arrested as part of an investigation into an extreme right-wing terror threat against the Islamic event.
Eight of those arrested remain in custody after officers secured warrants for their continued detention under section 41 of the Terrorism Act 2000.
The individuals include a 27-year-old arrested in Ipswich.
Others detained are a 27-year-old and a 29-year-old arrested in Surrey, a 35-year-old arrested in the Greater Manchester area, a 31-year-old arrested in east London, a 33-year-old arrested in southeast London, and two 42-year-olds arrested in Essex.
All eight will remain in custody for seven days.
All were arrested on Sunday, July 12, except for the men arrested in east and southeast London, who were detained on July 13.
Three further men, aged 55, 60, and 82, were arrested in Surrey on suspicion of conspiracy to murder.
They have since been released on bail.
A 48-year-old woman arrested in east London on suspicion of assisting an offender has also been released on bail.
The UK Ijtima event was cut short by organisers on Sunday following police advice.
