According to Tim Walker’s Mandrake column in the Sunday Telegraph, the BBC disinvited the historian William Shawcross from a debate at the behest of Tariq Ali.
“The two were due to debate the rights and wrongs of the Iraq war on BBC2’s breakfast news programme Weekend 24 yesterday with the affable presenter Simon McCoy. Then Ali seemingly had a hissy fit and said that if Shawcross was taking part he’d pull out.”
The BBC acquiesced. Malcolm Rifkind and Donald Anderson MP came on in place of Shawcross.
Sorry there is no link; I couldn’t find this online.