When, in 1946, the British colonial government officials in mandate Palestine were looking for a bright young Jewish scholar to take up a place at Cardiff University, they could scarcely have foreseen their choice would become a world-famous academic.

But they chose well in Czech-born Yehuda Bauer, now the doyen of Holocaust historians. Author of dozens of books about the greatest tragedy to befall the Jewish people, Professor Bauer is a barely believable 90, with the liveliest of minds. His conversation skips fluently from discussions of the Warsaw Ghetto to condemnation of Ken Livingstone, from social media to whether or not the Holocaust is unique.

Professor Bauer is the academic adviser to Yad Vashem and emeritus professor of Holocaust studies at the Hebrew University. In 1998, he was awarded the Israel Prize for his achievements in studying the history of the Jewish people. He was one of the editors of the Encyclopedia of the Holocaust and has been a consultant on many projects, including Claude Lanzmann's 1985 film, Shoah.

A long-time kibbutznik, he is famous among historians for regularly reviewing new evidence and revising his opinions about the Nazi genocide; and he is equally famous for his trenchant views, solidly backed up with decades of scholarship.

He has no hesitation, for example, in denouncing the former London mayor, Ken Livingstone, as "an extreme anti-Jewish and anti-Israeli propagandist who is misusing historical material to prove something that cannot be proved, because it is false".

He speaks Hebrew, English, German, Czech, Yiddish, Polish French and Slovak, of course

Mr Livingstone has been suspended from the Labour Party for claiming that Hitler supported Zionism and has previously cited an unsuccessful attempt by the Stern Gang to forge an alliance with the Nazis.

Professor Bauer, who has at home copies of the original correspondence between the Stern Gang, a Zionist paramilitary organisation, and Nazi officials, is scathing.

"So what?" he says, speaking at his hotel during a visit to London this week at the invitation of the Yachad group.

"The Stern Gang were about 120 people who were hunted by the Jewish population of Palestine at the time. It's like saying that [wartime fascist Sir Oswald] Mosley represented Britain. I won't debate with Livingstone. He has expressed views which have been rightly interpreted as anti-Jewish".

Professor Bauer was born in Prague in 1926 and, with his parents, made it to mandate Palestine in March 1939. Already a linguist, he learned his English from a New Zealand soldier on leave from the Western Front. "I introduced him to my parents and we were very friendly. Within six weeks, I could speak English".

Today, he says he speaks "Hebrew, English, German, Czech, Yiddish" - which he did not speak at home, but learned when at the Hebrew University - "and then I picked up Polish, French, Slovak, of course…"

Lisa, his daughter, who has accompanied him to London, intervenes to mention that he also plays guitar and sings folk songs in their original languages, including Welsh. It seems not so improbable when set beside his other accomplishments.

Before he arrived in Cardiff, Professor Bauer had served in the elite Palmach force - "using false identity cards" - and, when the War of Independence broke out, he interrupted his studies to fight in the new Israeli army.

When he resumed his work, he no longer had a scholarship, so had to make a bit of money first. He recalls with a huge grin: "I became a tourist guide, taking Jewish ladies wearing big hats with flowers, from Hadassah, round the Galilee."

The young Bauer completed his degree in Cardiff and spent a further year in Britain, working for the left-wing Zionist youth movement, Hashomer Hatzair. In 1952, he joined Kibbutz Shoval and picked up his studies again.

"Originally, my PhD was about the history of Zionism in World War Two but my great friend Abba Kovner [the poet and Holocaust-era partisan leader] persuaded me to change direction".

Professor Bauer became a Holocaust specialist and came to realise, he says, "that antisemitism was not only a part but the central part of Nazi ideology. Of course there were other factors, military, political, but the ideological factor was overriding."

Even in the last few years, he has continued to research and draw new conclusions about the way the Holocaust operated. In an important essay due to be published by Yad Vashem, he looks at the decisions taken by the Allies based on military priorities.

"America didn't have the Jews as a central issue on its mind, and even had it done so, there was no way of rescuing European Jewry. The Americans couldn't have done it, even if they had wanted to." Similarly, he dismisses the argument that the Allies could have bombed the concentration camps and saved Jews.

"People don't realise that no Allied planes bombed east Germany until 1943, simply because there were no fighter planes to accompany bombers. It was only at the end of 1943 that the Anglo-American B51 Mustang came into service, and it wasn't until then that they could have been used on any scale at all. These are military details which are crucial. There was simply no way to bomb anything in eastern Europe, never mind Auschwitz, until 1944".

But, he says, there was an instruction in January 1944 by the combined chiefs of staff of the Allies, "that all military units should not use air power to help people persecuted by the Nazis". It would have been a diversion of power and the losses would have been too great, said the chiefs of staff.

"They could have bombed Auschwitz [later in 1944] , and they invoked this ruling, and decided not to. And it would not have helped, because the Germans had other means with which to kill Jews after the gas ovens were closed at the end of October 1944".

For the Germans, he concludes, "the killing of Jews was a central thing. The fact that there were gas installations made it easier for them to do it. But the question - for the Allies - is moral. They knew what was happening, they could have changed the instruction, but they decided not to. The fact that they knew, and didn't act, is a moral blemish of the first order."

Despite everything that is known about the Holocaust, Professor Bauer continues to find information which "completely changes" his perceptions. He cited material found by a fellow historian in diaries from the Warsaw Ghetto.

"We are used to thinking that the Germans were cold-blooded murderers. That's a total error. The diaries show that in fact they were violent, brutal sadists who were emotionally involved in killing Jews".

He is very aware of the continued invocation of the Holocaust by politicians and others to suit their own agenda. He says: "It is the result of a trauma. It's not only the descendants of survivors, but people who have nothing to do with it from a family point of view. We [in Israel] are a traumatised society and we have politicians who constantly - and wrongly - compare the Holocaust with everything under the sun. You don't have one day in Israel without some reference to it, constantly."

But he says this is not special to Jews, and cites gypsies, Armenians, American Indians, Darfurians, as among those who have been traumatised by genocide. "They relate to it, usually by over-reaction and to things happening around them. As far as politicians are concerned, this is a misuse of the Holocaust.

"[Prime Minister] Netanyahu said the Nazis got the idea of murdering the Jews from the Mufti of Jerusalem, and had to retract. He actually believed it."

Professor Bauer said such analogies were also found on the left, citing the late Professor Yeshayahu Leibowitz, who had compared the Israeli army on the West Bank with the Nazi army. "All these analogies are false. The situation is completely different today. The 1930s are not the 2000s, there is the state of Israel and the Jews are not alone any more."

Nevertheless, Professor Bauer is quick to stamp on manifestations of post-Holocaust antisemitism, particularly recently, condemning the government of Poland for its new bill which would impose prison terms on anyone convicted of referring to the Nazi death camps as "Polish."

Claiming that the Poles collaborated with the Nazis in exterminating the Jews would also be a criminal offence. "They falsify history [with this bill]," he says. "The misuse of the Holocaust for contemporary political purposes is morally abominable and factually wrong".

Two things are uppermost in Professor's Bauer's mind as he enters his tenth decade. One is how the Holocaust will be reported and researched when all the survivors are gone; the other is the growing anti-liberal global movement, which he is at pains to counteract wherever he can.

Britain's loss of three major Jewish historians in the last two years - Martin Gilbert, Robert Wistrich and David Cesarani - was "a major problem", he says, although he notes there are currently 53 doctorates on the Holocaust being written worldwide.

He is keenly aware of the pervasive reach of the internet and social media and is alarmed at the level of hatred being disseminated there. "There are not enough companies who are dealing with the incitement to violence and the general trend of hate-mongering," he says. "Hatred is a major issue and we need an international coalition to fight it, and part of such hate-mongering is antisemitism."

Professor Bauer is often asked about the uniqueness of the Holocaust. He is clear that there have been other genocides since in many parts of the world. But for him, the uniqueness of the Shoah lies in the fact that it was the first such all-encompassing horror - and it remains, he believes, the measure for all other genocides.