Two sailors have been allowed to remain in the Royal Navy without being disciplined despite being named as members of a white nationalist group.

Mike Lynton and Kenneth McCourt were reported to have been members of Generation Identity, whose “great replacement” ideology was a key inspiration for the Christchurch massacre and other terror attacks.

An undercover journalist said they were serving together at a naval base in Plymouth, where they believed fellow sailors held similar views.

The journalist claimed Mr Lynton was the regional organiser for Generation Identity in southwest England at the time, and Mr McCourt was one of his recruits.

After his story was published in August, the Royal Navy promised an investigation but The Independent has learned that they were not disciplined.

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The case was dealt with “administratively” and the men were not put to a court martial.

They remain serving members of the Royal Navy after being referred to the government’s Prevent counter-extremism programme.

Generation Identity calls for a “remigration” of Muslims from Europe and spreads a conspiracy theory claiming that white people are being eradicated.

The theory’s name – the “great replacement” – was the title of a manifesto posted by Brenton Tarrant before the Christchurch shooting, which itself inspired several other terror attacks.

Tarrant donated money to the Austrian branch of Generation Identity and exchanged friendly emails with its leader Martin Sellner, who has been banned from entering Britain on security grounds.

At a briefing in September, police said far-right terrorism was the fastest-growing threat in the UK and named Generation Identity among groups able to inspire attacks, although it is not banned.

Ben van der Merwe, a journalist, said he met Mr Lynton and Mr McCourt while spending five months undercover in Generation Identity last year and described both men as “committed” activists.

“They weren’t dabbling,” he told The Independent. “Mike recruited Kenny on the base while they were serving, and Kenny told me about the lower-down ranks had sympathy with all of their views.”

Mr Van der Merwe, who conducted the investigation with campaign group Hope Not Hate, said Mr McCourt disclosed their roles to him at Generation Identity UK’s annual conference in July.

“Kenny told me that his superiors were aware of his involvement with Generation Identity, and said this meant if he got [a new posting] it was a good sign for the group in terms of future activity in the navy,” he said. “He said all the officers were racist, including his diversity officer.”

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Mr McCourt also allegedly claimed to be friends with a neo-Nazi YouTuber called Eternal Reich.

Mr Lynton was more senior in Generation Identity and organised events and recruitment, according to Mr Van der Merwe.

He is said to have targeted meetings of Ukip’s Young Independence youth wing looking for potential members.

Mr Van der Merwe said he had not been contacted by the navy with any request for information, despite possessing detailed notes of conversations and other evidence that had not been published.

He said that relying on publicly available material for the internal investigation amounted to a “whitewash”, adding: “It doesn’t give off the impression that it was a serious attempt to get to the bottom of what their activities were or the extent of far-right extremism in the navy.”

The revelations follow the imprisonment of a British Army soldier who was a member of the banned neo-Nazi terrorist group National Action.

Through his work as an army trainer, Lance Corporal Mikko Vehvilainen tried to bring what he called “committed Nazis” over to the organisation.

But his conviction in 2018 is not known to have sparked proactive attempts to detect and root out far-right extremism in the armed forces.

Mr Van der Merwe called the situation a “time bomb”, warning: “These are people with military skills, access to weapons and the ability to commit attacks.”

Generation Identity UK rebranded itself to become the Identitarian Movement late last year following infighting over speakers at the conference.

Leaders of European factions publicly distanced themselves over the appearance of “alt-right YouTubers” at the event, and defended its activism as legitimate concern over the alleged cultural and ethnic “replacement” of “indigenous Europeans”.

Former UK leader Ben Jones claimed the Identitarian Movement was “free of violent tendencies and has never committed any violent acts”.

But a statement released last August admitted: “Certain people associated with our organisation serve in the navy and indeed, on submarines.”

The British branch continued publicity stunts, including mock executions of anti-racist activists, until it was dissolved in January.

“Rather than being the end of a story, it represents the beginning,” Mr Jones wrote in a message to supporters.

A navy spokesperson said: “Extremist ideology is completely at odds with the values of our armed forces and we take allegations of this nature very seriously.