An insight into the political convictions and electoral strategy of Nick Griffin at the point at which he took control of the British National party (BNP) has been disclosed with the release of a series of documents, including police interviews, concerning his prosecution on race hate charges in the late 1990s.

The papers, from the Crown Prosecution Service, illustrate how Griffin believed the Holocaust did not happen, was convinced that multi-culturalism was the result of a plot by international capitalism and Zionism and held the wish to win political power so as to "peacefully and humanely as possible" recreate Britain as an overwhelmingly white nation.

Griffin, who in this month's elections is fighting to retain the European parliament seat he won in 2009, also talks about how the British mass media was "greatly controlled" by what he calls "organised Jewry" and how many of the films made in Hollywood, including Steven Spielberg's, are "anti-white" propaganda.

The documents, obtained under the Freedom of Information Act, also show that Griffin believed it was possible for him and like-minded individuals to take power in Britain by developing a political party with broad appeal and the capacity to mount well run election campaigns.

The papers include transcripts of police interviews with Griffin before he was charged under the Public Order Act with publishing a magazine likely to stir up racial hatred. In 1998 he was tried and convicted and received a nine-month suspended prison sentence.

The following year he came to the public's attention for the first time when he was elected leader of the BNP.

He immediately began to attempt to transform the BNP's image from that of a thuggish neo-Nazi movement to a party that embraced populist rightwing policies, such as withdrawal from the EU and restrictions on immigration. The party's latest campaign highlights the danger it claims Britain's seal population faces because of Brussels' fisheries policy.

Griffin was elected in 2009 as a member of the European parliament for north-west England after the BNP polled 132,000 votes, 8% of the total, on a turnout of 32%. At the next election he is expected to face greater pressure from the UK Independence party (Ukip), and some observers are predicting a slump in the BNP's vote.

The question of whether Griffin ever genuinely shed his antisemitic views is difficult to answer. Shortly before he became the BNP's leader he said he hoped to learn from past mistakes such as letting his "youthful enthusiasm for perfect ideas to run far beyond what's politically possible".

Protesters at BBC Television Centre on 22 October 2009, before Nick Griffin was due to appear on Question Time. Photograph: Peter Macdiarmid/Getty Images

In 2009, during an appearance on the BBC's Question Time, he struggled to explain his views on the Holocaust. David Dimbleby asked whether he had denied it, to which he replied: "I do not have a conviction for Holocaust denial."

Asked last month whether he continued to believe the Holocaust did not happen, his press officer, Simon Darby, said: "It's old hat, he won't talk about that. It's irrelevant. Are you Jewish yourself? It's a non-story."

Darby added that Griffin would not answer questions on his beliefs because "you have never given him a fair crack of the whip – you will only distort what he said". Griffin did not respond to emailed questions.

The papers were obtained under FoI from the CPS. The CPS spent more than two years trying to prevent their release, arguing at one point that the information was Griffin's sensitive personal data.

The documents were released after the Information Tribunal ruled (pdf) that disclosure was in the "substantial public interest".

The papers include a statement from a police officer who overheard Griffin take a phone call while police searched his home near Welshpool on the English-Welsh border. The officer said: "I … heard him say to this unknown caller 'they're very civilised, more civilised than the Met [Metropolitan police], no Jews or Pakis.'"

While being interviewed under caution by two detectives at Welshpool police station later that day, Griffin said the purpose of everything he did could be summed up in one sentence: "We must secure the existence of our race and a future for white children." This is a slogan known as the Fourteen Words, which is popular with white supremacist groups in the US.

He added: "Everything I do is related to building a nationalist movement through which peaceful persuasion and through the ballot box can place us in a position whereby those 14 words can be carried out."

Griffin said there were some British nationalists who believed they should resort to violence. "There are some people who are saying, 'the IRA has got a long way in Ulster … by killing people, so that is what we should do.'" He believed, however, that the British far-right should study the example set by the Front National in France, which was beginning to make significant electoral inroads. "They're coming towards political power through the ballot box. So I'm saying it is possible."

Nick Griffin: 'Our grandchildren will be a mass of mongrel slaves, if things are not reversed.' Photograph: Dave Thompson/PA

Griffin also told the police that he believed that "by the end of the next century the white race will be headed inevitably for extinction"; that he did not wish to see large numbers of people "from any ethnic group other than British and European stock" residing in the UK; and that while he had "no antipathy to Jews, as Jews", he believed they had too much control of the British media.

"It's not a belief, for example, that organised Jewry has a massively disproportionate hold on the mass media; it's a fact," he said. "It is my belief that what the mass media is doing in terms of propaganda in this country is overwhelmingly harmful."

He also had a problem with Hollywood, which he said had produced "about 550 grotesquely anti-white films" over the previous 30 or 40 years. He was particularly upset by the director Steven Spielberg, whom he accused of making films that were "fundamentally anti-white propaganda and lying propaganda at that".

The detectives questioned Griffin about a passage he had written in a BNP magazine called Rune which referred to a "final victory over those who seek to destroy us so that they can rule unchallenged forever over a mass of mongrel slaves". Asked to whom he was referring, Griffin replied: "International capitalism and international Zionism."

Questioned further, he added: "Our grandchildren will be a mass of mongrel slaves, if things are not reversed. If a movement dedicated to preserving the white peoples of the west in their own countries does not come to power then within a very short space of time historically, the white race will cease to exist."

One of the officers, a detective constable, noted that Griffin had written about "winning", and asked: "What would winning mean to you?" Griffin replied: "Taking political power so as to be able to institute changes, to undo the population shift which has taken place since 1948 with the first Immigration Act, to peacefully and as humanely as possible reverse that and to return Britain to being a homogeneous white nation."

The officers then moved on to the Holocaust. Griffin told them: "My views are that very large numbers of Jews, certainly, almost certainly hundreds of thousands, were killed during the war for no other reason but that they were Jewish. In the same way that several million Germans were killed for no other reason but that they were German and the people of Hiroshima and Nagasaki were killed for no other reason than that they were Japanese. If you end up with a full-scale war then huge numbers of innocent people are killed.

"But the allegation that there was a systematic and deliberate policy whereby six million Jews were gassed to death is for a variety of forensic and common sense reasons, utter nonsense."

To think otherwise, Griffin said, was like believing the sun revolved around the earth. He added: "I will be delighted if this does come to court to … discuss the question of … the lie of the six million, at length."

Asked towards the end of the interview to reiterate his political motives, he replied: "Fourteen words."

No press or independent observers were present when Griffin appeared at Harrow crown court. One prosecution lawyer recalls that Griffin sacked his defence team, then defended himself on the basis that the contents of Rune were justified. The jury found him guilty.

On subsequently becoming leader of the BNP Griffin gave a speech in the US to American and European far-right activists in which he spoke about his conviction and warned his audience against going too far with their "revisionist" claims about the Holocaust.

Meanwhile, BNP activists were warned against displays of the "three Hs", which Griffin defined as hobbyism, hard talk and Hitler, and were encouraged to characterise themselves as defenders of free speech against a politically correct liberal establishment.

In recent months, however, Griffin appears to have returned to the theme that emerged during his police interviews. In a speech at the European parliament in March, he said he believed "an unholy alliance of leftists, capitalists and Zionist supremacists have schemed to promote immigration and miscegenation".

Their purpose, he added – in a speech that could be one of his last to the parliament – was to "breed us out of existence".

Nick Griffin timeline

1972 Joins National Front at the age of 14 and remains a member until 1989.

1995 Joins the British National party.

1998 Receives nine-month suspended sentence under Public Order Act for publishing magazine likely to stir up racial hatred.

1999 Replaces John Tyndall as leader of the BNP.

2005 BNP contests 119 seats at general election but wins none. Increases votes from 47,219 in 2001 to 192,850.

2006 Griffin and Mark Collett cleared of inciting racial hatred in speeches.

2009 Griffin and Andrew Brons elected to European parliament for BNP.

Luc Torres