In a blog post on the Grousebeater website, Campbell Martin said his old party had been “completely compromised”.
“It was and remains insane to believe that the British state had not infiltrated the SNP,” he wrote. “A political party that claimed its raison d’être was the collapse of the British state.”
The Interior Ministry has so far refused to comment on the allegation.
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Mr Martin’s accusation comes just days after it was revealed that, thanks to moles, security services were able to identify the four young nationalists who liberated the Stone of Destiny in 1950.
Recently declassified documents revealed that Special Branch detectives in Scotland used whistleblowers to find out who was behind the robbery.
In his blog post, Mr Martin wrote: “British officials in the SNP have risen through the ranks over the years and now hold senior positions that have enabled them to influence the policy and direction of the party, for example by taking on a Series of senior positions.” Urgency in achieving independence… and that’s putting it mildly.”
He added: “The SNP is completely compromised, it has been captured and controlled by the British state.”
Mr Martin said the UK state had “played a dud”.
“Today’s SNP is so corrupted by British agents that it ignores independence and pursues gender politics that make the party unelectable. For the British state that is done.”
Mr Martn was an SNP MP between 2003 and 2004. He was disfellowshipped after criticizing John Swinney’s leadership.
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He said it was not unreasonable to suggest an infiltration of the SNP as the intelligence agencies had managed to penetrate the IRA, the National Union of Miners and the Socialist Worker Party.
“It would be even more extraordinary if they ignored the SNP, a party that supposedly wants to crush the British state,” he said. “If they hadn’t infiltrated this organization, something would be very wrong.”
Jim Sillars, who was deputy leader of the SNP in the 1990s, is also convinced that British agents operate within the party.
He told The Times: “When I came on in 1980, Dr. Robert McIntyre [the party’s then president and first MP] He came up to me and said, ‘Do you realize we’re all being penetrated?'” he said.
“Indeed, given my Labor background, there was some suspicion that I might be one of the intruders. The big problem we have is figuring out how deep the infiltration goes and how high it goes.”
Mr Sillars said he and his late wife Margo MacDonald, the former SNP MP and independent MSP, “simply accepted” that some supposed comrades were double agents. “There were a couple of people in the group who I was absolutely certain were MI5 agents,” he said. “We can not do anything about it.
“We are a constitutional national organization and as such have never established a counterintelligence department within the party.”
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Alex Neil, who served as Health Secretary in the Salmond Government and resigned as MSP in 2021, also believes the security services are operating covertly within the Scottish Government.
“If I were the first minister, I would assume there are people from within the organization who are out to finish us off,” he said. “Who they are, who they employ, what they actually do, what positions they hold and how many there are, we just don’t know.
“I have no doubt that in the decades to come, as official secrets emerge, it will become clear that the people who reclaimed the Stone of Destiny were not the only ones betrayed by people who believed in them were faithful to the cause.”
The SNP and the Interior Ministry have been asked for comment.