Papers from the 1960s reveal official scepticism about the activities of the Free Wales Army (FWA) and a reluctance to give them publicity.
Cayo Evans was imprisoned for public order offences in 1969
The FWA's declared aim was to start a revolution which would lead to independence for Wales.
But files from the National Archives in Kew show that leader Julian Cayo Evans was described by authorities as having "a mental age of about 12 years".
Evans and sidekick Dennis Coslett were later jailed for public order offences.
They were sent to prison for 15 months in 1969, on the same day as the investiture of the Prince of Wales in Caernarfon Castle.
Monday marked 10 years since Evans died, and more than four decades since the FWA began seeking publicity against a background of a volatile political atmosphere.
Anger had been provoked among Welsh nationalists in the late 1950s by the decision to flood a valley in Gwynedd to provide water for Liverpool.
Despite public protests - including action by FWA members - and the opposition of Welsh MPs, Tryweryn dam was built.
There were a number of explosions, not all connected with Tryweryn.
Although these blasts were never officially linked to the FWA, former soldier Evans regularly appeared with a gang of uniformed men, boasting hundreds of troops at his disposal - in reality not numbering more than about 20.
Historian Dr John Davies said the description of Cayo as having a mental age of 12 was "a bit unkind".
"He was certainly a fantasist," Dr Davies said.
He added that even though the FWA was "a manufactured movement to some extent", the government was obviously concerned enough to investigate it thoroughly.
"The essential background was Ireland - I do not think that there was any possibility that developments in Wales would take the same path as those in Ireland, but the authorities were being sensitive on the matter," he said.
The documents in the National Archive show that police investigated their activities very closely after a magazine article in 1967, which showed a series of pictures of the FWA "on exercise" with dramatic straplines including "the weapons are real" and "IRA tactics turn up in Wales".
The 1967 article prompted a great deal of interest from the authorities
The papers reveal that the piece, in Town magazine, was brought to the attention of the attorney general by MP Emlyn Hooson, who asked whether there were grounds for possible proceedings under the Public Order Act.
The article's writer Bryn Griffiths was interviewed by a Sergeant Tucker of the Metropolitan Police.
Sgt Tucker said Mr Griffiths could not be certain real weapons had been involved in the exercises, and that some of those involved had been recruited just for the pictures.
'A staged show'
A memorandum by the director of public prosecutions then stated there were two possible grounds for prosecution but discounted both.
The first was over the uniforms being worn in a public place. However, since the photos were taken on Cayo Evans' farm, this did not apply.
The second was over the training, which could have violated the act if members were being "organised and trained...for the purpose of enabling them to be employed for the use or display of physical force in promoting any political object."
This memorandum advised against prosecuting the FWA
But the memo stated that the article had been "a staged show and that eight of the persons shown...had been recruited to pose for the photographs in uniforms loaned to them for the purpose".
The findings concluded against "taking the organisation's activities too seriously," saying this "would give to it an unmerited importance and publicity which its leaders are plainly seeking".
In the background information, Evans was described as having "an undeveloped personality and his mental age is about 12 years".
And his second-in-command Dennis Coslett, who died in 2004, was described as "an unbalanced personality" who "can be violent".
"He is an object of derision and fun at Llangennech and receives little support," it added.
However, under pressure to do something about the protests against the investiture, the police in Wales did arrest nine FWA members in dawn raids.
When Evans and Coslett were put on trial, evidence provided by the journalists they had courted for publicity helped secure their convictions.