The arrests include people aged between 22 and 35 - of which six were nabbed from northwest England, two from South Wales, one from Wiltshire, and two from West Yorkshire, the Metropolitan Police said.
Eleven properties are being searched across England and Wales as part of the investigation led by Counter Terrorism Policing North East and North West.
The arrests were a result of two separate investigations coordinated across a number of police forces, according to the Met's Neil Basu, senior national coordinator for counter- terrorism policing.
"Today's arrests, while resulting from two separate investigations, have been coordinated by our officers across a number of forces. This maximises operational effectiveness for police and minimises disruption for the local communities," he said.
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All those arrested are suspected to be members of National Action and of them six are also being questioned on suspicion of preparing acts of terrorism and five are suspected of funding terrorism.
National Action, an anti-semitic, white supremacist group, was banned as a terrorist organisation in December by Home Secretary Amber Rudd, who described it as "a racist, anti-Semitic and homophobic organisation" at the time.
The arrests follow activity earlier this month by the West Midlands counter-terrorism unit, which resulted in three men, including two British soldiers, appearing in court, accused of being members of National Action.
A spokesperson said, "No serving armed forces personnel or veterans were arrested today by civil police as part of their coordinated activity against proscribed organisations".
Being a member of - or inviting support for - a proscribed organisation is a criminal offence carrying a sentence of up to 10 years in prison.
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