This week, I tell the tale of two historians. Professor Ilan Pappe holds a DPhil from the University of Oxford. Professor Benny Morris holds a PhD from the University of Cambridge. Morris currently teaches at Ben-Gurion University, Beersheva. Pappe used to teach at Haifa University but five years ago managed to arrange a transfer to the University of Exeter.

Both Morris and Pappe are "revisionists". Broadly speaking, the revisionist position may be summarised thus: Palestine a century ago was not "a land without a people". It was inhabited by Arabs, whose Muslim majority had lived for centuries in harmony with small Christian and Jewish minorities. But then the Zionists, in league with the British imperial establishment, conceived a dastardly plan to "ethnically cleanse" these peace-loving Arabs and replace them with a Jewish majority. In 1947-48 this plan reached its bloody climax. Through organised mayhem and massacre, the Arabs were driven into exile, and the "colonialist" Jewish state came into being.

I gave this explanation of Zionist revisionism in my column of May 30 2008. The purpose of that column was to announce that Benny Morris, the left-wing revisionist who had in 1988 gone to prison rather than heed a call-up for reserve duty during the so-called First Intifada, and whose monograph, The Birth of the Palestinian Refugee Problem, published the same year, may be said to have been one of the founding documents of Zionist revisionism, had begun to repent.

I drew attention to a Newsweek article in which Morris declared: "It has become clear to me that, from its start, the struggle against the Zionist enterprise wasn't merely a national conflict between two peoples over a piece of territory, but also a religious crusade."

I explained that Morris had finally accepted the existence of what I described as "an unbroken thread linking the anti-Jewish and pro-Nazi sentiments of Haj Amin al-Husayni, Grand Mufti of Jerusalem in the 1930s and 1940s, and the anti-Jewish verbiage of the founding charter of Hamas." Escalating and religiously driven Arab violence against Jews formed the backcloth against which Haganah actions against Arab villages in 1948 must be understood and judged. Once expelled, the inhabitants of these villages were not permitted to return - as Morris himself has said, they were regarded as a potential fifth column.

Cambridge's Morris has recanted Oxford's Pappe has not

But while the Cambridge-trained Benny Morris has recanted, the Oxford-trained Ilan Pappe has not. Quite the reverse. Safely ensconced in the West Country, Pappe has transformed himself from an academic pure and simple into a political propagandist of the extreme anti-Zionist variety.

It is no exaggeration to say that his Ethnic Cleansing of Palestine, published in 2006, has become a core text of the revisionist camp, and a work of seminal reference for the movement to delegitimise the Jewish state. His autobiographical Out of the Frame, published last October, seeks to build upon this reputation by effecting to chart and justify his break with Israel and his espousal of the "one-state" solution.

In the American fortnightly journal New Republic on March 17, Benny Morris treats us to a meticulous analysis of these two works, and of a third, Pappe's account of The Rise and Fall of a Palestinian Dynasty: The Husaynis 1700–1984. In dissecting these works, Morris has - commendably - not relied on Pappe's explanation of the documents he has used, but has gone back to the documents themselves, and has evaluated them alongside others that Pappe might have used but for some reason chose not to (for example, the archives of the Ottoman Empire).

We are not talking here simply of slips of the historian's tongue (such as the confusion of Prime Minister Ramsay Macdonald with his son Malcolm, author of the infamous white paper of 1939 that sought to bring to an end Britain's obligations under the Balfour Declaration).

Rather, Morris presents us with a damning indictment of a historian whom he accuses of grossly distorting the documentary evidence to suit an ulterior political purpose. "At best", Morris declares, "Ilan Pappe must be one of the world's sloppiest historians; at worst, one of the most dishonest."

Pappe tells me his "inclination" is not to reply to the charges Morris has levelled at him. But unless Pappe offers a very robust defence indeed, his credibility as a serious historian must be irreparably damaged. Don't take my word for this. Go online (at tnr.com ) and read Morris's indictment for yourself. It is entitled The Liar as Hero.