I looked up the number further, and the numbers they give are for deaths by malnutrition and disease, not military action. Those dying in the flu pandemic are excluded, though it says nothing about the encephalitis epidemic that was pretty deadly and overlapped World War I a bit. In any case, during World War II, antibiotics were available to treat people who had diseases. But they were not around (sulfa drugs could help with infection but were not nearly as effective as antibiotics) for World War I. So in World War I, a larger percentage of people would have died of infection than in World War II. Tuberculosis, in particular, was a scourge that killed a lot of people before antibiotics.

Deaths caused directly by military action in the First World War were far lower than the Second; the War Office compiled Statistics of the military effort of the British Empire during the Great War, 1914-1920 with a section on [Airship and Aeroplane Raids Over Great Britain, and Bombardments of the Coast, with the resulting Casualties] (https://archive.org/stream/statisticsofmili00grea#page/674/mode/2up). Total casualties (both military and civilian) are given as 1,570 killed, 4,041 injured. It also lists Mercantile Marine casualties as 14,661 dead. Larger numbers may include deaths from malnutrition or disease.

In the Second World War, UK civilian deaths are typically estimated to be around 62,000, about 40,000 of those from air raids, the remainder at sea, in internment camps etc.