British police said six people had been arrested by counter-terrorism officers on Wednesday on suspicion of being members of the banned far-right group National Action.
Five men in their twenties and a 37-year-old woman from across central and northern England were held under anti-terrorism legislation and several properties were being searched.
The neo-Nazi group became the first far-right organisation to be outlawed in Britain in 2016 after the murder of Member of Parliament Jo Cox, whose killing it had praised.
Last year, a man accused of being a member of the group appeared in court accused of plotting to murder another politician, and soldiers have been among those previously arrested as suspected National Action members.
Police said the latest arrests were pre-planned and there was no threat to public safety.