Irving told The Telegraph that Williamson, recently forced to return to England from Argentina, got in touch with him by e-mail.
"He is obviously a very intelligent man who did not realize the danger of talking to the press," Irving said. "He is not a Holocaust denier. Like me, he does not buy the whole package."
In an interview with a Swedish TV station, Williamson said the evidence shows that about 300,000 Jews died in Nazi concentration camps and that none of them were killed in gas chambers. Most historians agree that 6 million to 7 million Jews died in the camps, along with millions of Gypsies, Communists, homosexuals and the disabled.
A few days later, Pope Benedict XVI announced that he was lifting Williamson's excommunication. The pope, since then, has told Williamson he must publicly recant his views on the Holocaust if he wants to return to full communion.
Williamson had been living in a traditionalist seminary in Argentina but was ordered out of the country last week.