Commander Richard Smith, head of the Met’s counter-terrorism unit, said it was a “unique” case and that there was no evidence Hannam abused his position “to further his extremist views”.
The ideology of National Action was described in court as based on “Aryan purity” and a hatred of non-white groups, particularly Jews.
“He would never have been able to join had we known then of his interest in the extreme right wing and his previous membership of National Action,” Smith said.
Police found neo-Nazi posters when they raided Hannam’s home last year, as well as notes detailing his membership of the group and related badges and business cards.
In his defence, Hannam denied he had ever been a member of the group before or after it was banned, and said that he had been “desperate to impress” an older member at the organisation, who had given him free stickers and badges.
He told the court he had been attracted to fascism aged 16 because of its bold artwork and contacted National Action after seeing its propaganda online.
“I was under the impression this was some kind of youth network,” he said.