British historian David Irving has said he is the victim of a "world-wide attempt to silence" him.
David Irving complains he was jailed for expressing "wrong views"
He is back in the UK after his release on probation from a three-year jail term imposed in Austria for denying the Holocaust in a 1989 speech.
Mr Irving said "Stalinist legislation" had put him in prison for expressing the "wrong views" about history.
At his trial in February, he said his views on the Holocaust had changed, but did believe it had been exaggerated.
The conviction had sparked intense debate, with supporters saying it was fully justified but opponents arguing it undermined the right of freedom of speech.
In his speech in Austria 17 years ago, he denied the existence of gas chambers at Auschwitz, though he later said he was "mistaken".
He told his initial trial that Auschwitz's role as a "killing centre" has been exaggerated to pander to the tourist trade.
At a London news conference on Friday, Mr Irving said he had been treated "with utmost contempt" in Austria and Germany.
He called for an international boycott of all historians in the nations until they put pressure on their governments to change laws.
The 68-year-old insisted he was not a "Holocaust denier".
"For the last 15 years, I have made no bones at all about the fact that the Nazis killed millions of Jews in different methods around the world, around their empire, particularly on the Eastern Front," he said.
"And I've published documents that none of the conformist historians have bothered to find."
Mr Irving served 13 months of his sentence and has now been banned from Austria. The 1992 law targets "whoever denies, grossly plays down, approves or tries to excuse the National Socialist genocide".
But his release on probation has dismayed Jewish groups.
Lord Janner, vice-president of the World Jewish Congress and president of the Commonwealth Jewish Council, said: "I do not believe that he was put in prison because he was a historian. And historians should be treated in the same way as anyone else."
Karen Pollock from the UK-based Holocaust Education Trust said: "We are reminded of the need to remain vigilant to ensure that Holocaust denial, in whatever guise it appears, is challenged."