The 1919 Holland Report does not agree with that conclusion.
"Ample and generous provision must be made for the continuous study of chemical warfare both as regards offence and defence during peace, in order to ensure the future safety of the fighting forces of the Empire."
The use of chemical weapons in WW2 was only ever seriously considered by the British, though its use was anticipated by all sides and it would be naive to think that other nations were not prepared to use them. The RAF trained extensively in 1940 in order to be able to attack any German landings with mustard gas and, lesser known, to attack the German civilian population with phosgene.
The RAF established a committee to deal with the use of chemical weapons in September 1940. At the very first meting the use of phosgene against German civilians was discussed, described as
" ...a very suitable weapon against the German civilian population"
particularly because so few German civilians, in contrast to the British, had gas masks.
By this time the RAF had already developed its 'Gas Plan'. Sixteen squadrons within Bomber Command were designated for dropping chemical ordnance onto, or spraying chemical agents over any invading forces. Until an emergency arose these squadrons would carry out their normal duties. Slessor (then director of RAF Plans) wrote to Brooke.
"It is not present policy that squadrons should stand by to use gas against enemy landings. If the use of gas is authorised after invasion has taken place, an interval of 24 hours will be required to change over from bombing to gas spray."
In fact the five squadrons of Lysanders among the designated sprayers could be ready in six hours. Slessor also confirmed that station commanders and enough pilots were trained in the use of gas. He also wrote that
"...it was feasible for orders for gas spray to be given in the same manner as for the bombing of targets. It is not considered necessary to introduce a special code word for the use of gas, since we are operating in our own country and such orders will have been issued before the aircraft take off."
Initially, as of June 1940, stocks of gas were only sufficient for two days of intensive operations, but production was rapidly increased. By September 27th 350 tons of mustard gas and 45 tons of phosgene were being produced every week and stocks had risen to 13,000 tons. Storage for a 4,000 ton reserve was nearing completion.
Spraying was a preferred method of achieveing high concentrations of gas, but the RAF was well aware that low altitudes gave better results, but also made the aircraft much more vulnerable. Large numbers of 250lb and 30lb bomb cases were avialable, and were filled through the summer of 1940 with mustard gas. This agent was preferred for its persistence, and ability to contaminate the ground, equipment and clothing of the enemy, forcing them to wear respirators. One 30lb mustard gas bomb could 'heavily contaminate' an area of 50 square yards, with 'lighter contamination' spreading over 300 square yards.
There is a common misconception that the British would have been constrained by some kind of moral scruples in their fight for survival. We might ask a survivor from the French Mediterranean Fleet about that. I have seen it argued that men who had seen the effects of gas, or been gassed themselves, in WW1 had a reluctance to use such weapons again. From a British perspective this is palpable nonsense. There was a debate about the morals of the FIRST USE of chemical weapons, but it was won by the pro-use faction, behind who Churchill threw his weight. The pro lobby was led by the CIGS, Sir John Dill, and this is one thing on which he and Churchill did agree. I have no doubt at all that if, by some miracle, a German beachhead had been established on British soil in 1940/41 it would have been attacked with chemical weapons. The landings never happened, and the 'Gas Plan' was never put to the test.
The Army had ten companies trained in the use of gas and substantial stocks. 12,000 x 4.5", 13,000 x 6", 15,000 x 6lb 'ground bombs' all filled with mustard gas along with 1,000 chemical mines, each containing 4 gallons of mustard gas. there were also ten 'Bulk Contamination Vehicles' available, each carrying 130 gallons of gas, designed to contaminate the ground in a withdrawal. 950 WW1 vintage Livens Projectors were resurrected from stores, one of the most effective way of delivering high concentrations of gasses, out to about a mile, developed in WW1, but only effective when dug into a defensive line, like the Royal Military Canal.
The principal reason they were not used later in the war was that other and more reliable solutions to the military problems in which chemical attacks were deemed effective in WW1 had been developed.
Cheers
Steve