Do you mean the 1918 flu pandemic? There is some limited evidence of it circulating from 1915, but it really took hold from 1918 and then continued into 1920 - a period of time marked by the large scale movement of troops and displaced persons.
When there is an inquiry into the impact of and response to Covid in the UK the picture will be one of multiple introductions into a densely populated island by returning holidaymakers (including large numbers of skiiers returning from Europe) and business travellers.
Some people will still go on about Cheltenham though.