Follow-up question: I know that he isn't a reputable historian, but is David Irving even considered to be a historian? Professor Richard Evans, whose report that was compiled for the famous libel case against Irving is quoted in this BBC profile, stated that:

Irving has fallen so far short of the standards of scholarship customary amongst historians that he does not deserve to be called a historian at all.

There is a FAQ section on Holocaust Denial which may be of interest to you, though it may not directly address your question.