LONDON—A gang of British soldiers has been arrested after security services allegedly caught them preparing or instigating acts of terror as part of a neo-Nazi group that has been banned in Britain.

The discovery of an alleged far-right terror group operating inside the Army threatens to undo decades of hard work and retraining that went into ending the stereotype of racist squaddies and institutionalized prejudice in the British Army.

The four men were allegedly members of National Action, a racist and anti-Semitic organization that was proscribed as a terrorist group last year. Members have been filmed at rallies throwing Nazi salutes while dressed in black and waving banners proclaiming “Hitler was right.”

The group, which allegedly trains its members in combat techniques, adopted the slogan “Death to traitors, freedom for Britain” in honor of Thomas Mair, the right-wing terrorist who murdered British politician Jo Cox during the Brexit referendum campaign.

The four men, aged between 22 and 32, were arrested by a counterterror unit “on suspicion of being concerned in the commission, preparation, and instigation of acts of terrorism,” a police spokesman said, adding they were suspected members of the terror group.

National Action was the first right-wing organization to be banned in Britain since World War II, when Oswald Mosley’s “blackshirts” were proscribed. “National Action is a racist, anti-Semitic, and homophobic organization, which stirs up hatred, glorifies violence and promotes a vile ideology,” said Amber Rudd, the Home Secretary, when she banned it last year. “The safety and security of our families, communities, and country comes first.”

The four service personnel are being held at a police station in the Midlands while officers search addresses linked to them. “The arrests were pre-planned and intelligence-led; there was no threat to the public’s safety,” said a spokesman for the West Midlands police, suggesting that they had been under surveillance for some time.

The Ministry of Defence confirmed that four servicemen had been arrested and said they had co-operated with the security services’ operation to catch the alleged terrorists.

National Action, which dedicated itself to attracting young recruits from universities, praised the assassination of Cox, who was shot dead in the street in Northern England last year, posting a message that read: “Our thoughts go out to Thomas Mair #Britain-First #JoCoxMP” and, “Don't let this man’s sacrifice go in vain. #JoCox would have filled Yorkshire with more subhumans.”

The group also reportedly saluted Anders Breivik, the Christian terrorist who murdered 87 people in Norway in 2011, and Timothy McVeigh, the Oklahoma City bomber who killed 168 people in 1995.

Research by Hope Not Hate has linked Benjamin Raymond, who used the name Benjamin Noyles, to hate groups in the U.S., including American Renaissance Party of North America.

Benjamin was named after an investigation by the Sunday Mirror, which quoted a Facebook post made when George Zimmerman was acquitted of murder charges for shooting Trayvon Martin in Florida. “It’s now legal to kill n******!! They are all out and armed. Shoot them on sight!” he wrote.

Another outspoken member, Jack Renshaw, has been caught on camera claiming he is a “good shot” and warning that “There will be violence” if immigration into Britain continues.

“These invaders, these parasites, they’re not just going to roll over and let us remove them from our country. They will put up a fight and we need the killer instinct,” he says in footage obtained by the Sun.

Members of the group posted photographs on social media that apparently showed them giving Nazi salutes at the Buchenwald concentration camp in Germany.

The British Army will now be forced to explain how men which such sickening links could have been allowed to infiltrate the armed services.