If chemical weapons are so useless how did Saddam manage to kill so many, so effectively, in Halabja, March 16, 1988? Overall more than 40 Kurdish villages were attacked. According to our 'expert' (who, to me, sounds very blase about the whole thing, which he shouldn't - Porton Down were cowboys before the 90's) death on such a scale should be impossible unless a totally disproportionate amount of chemicals were used.
The other point which he fails to address, which is taught throughout the services during basic NBC training, is how chemical weapons come into their own when the attacking force wishes to take the enemy area without damaging it. Levelling an area may kill the enemy but all you win is the land it was built on. Maybe the army needs more property developers...?