When it comes to Irving the question ,as Deborah Lipstadt points out--via Clive, is not about intelligence but knowledge. Those listening to him won't be able to hold him to account for his views, as they won't know where the holes in his argument are and when he is dissembling about what a document says.
Julian Lewis was particularly eloquent on the platform question on the Today Programme this morning. But his principled decision to resign from the Oxford Union over the invite could, though, put some of his fellow MPs in a rather difficult position. There must be quite a few MPs, the majority of them Tory I suspect, who are life members of the Union. Are they all now going to come under pressure to resign?