The brewer’s favourite adjunct soon had to be dropped, I assume for pure supply reasons. Maize not being grown in the UK at the time, it had to be imported. Which was always going to be problematic, when there were other priorities for scarce transatlantic transport.
Almost immediately following the outbreak of war, there were restrictions on the raw materials available to brewers.
"At the outbreak of war every brewer realised that he would be forced to make drastic alterations in the composition of his grist, for he was forbidden to use flaked maize, future supplies of barley from Central Europe was cut off, while available supplies of Californian malt were materially reduced and in some cases ceased entirely while there was a possibility that sugar would be rationed.
It is probable that flaked maize has been used more from the view of economy than anything else, and its effect on the composition of the wort is hardly of sufficient importance to present any difficulty in replacing it. Flaked rice in limited amount is still available, however, and can easily replace flaked maize although it is quite possible that it may be restricted in the future."
Journal of the Institute of Brewing Volume 46, Issue 4, August 1940, page 274.
Flaked maize disappeared in 1940, initially replaced by flaked rice and later by flaked barley. It only made a reappearance in the early 1950s, when it quickly regained its pre-war position as brewers’ favourite adjunct.
A few brewers preferred grist over flaked maize, though this this was definitely the exception. Presumably because an extra piece of equipment – a cereal cooker – was required.
William Younger of Edinburgh was an enthusiastic user of grits. It often made up over 40% of their grists. Barclay Perkins also used grits, but only in some of their Lagers. Never in their other beers.
Unlike flaked maize, grits didn’t disappear from brewing records in 1940. They hung around until early 1942 in William Younger’s brewing records. Though they were then definitively dropped by the brewer. Once the most enthusiastic user of grits, William Younger never returned to them. Preferring, when maize became available again in 1949, to use them in flaked form, like everyone else.