The first world war barely registers on the graph. The second world war shows a small decrease in population. But the largest decrease is seen in the 70s and 80

The first world war barely registers on the graph. The second world war shows a small decrease in population. But the largest decrease is seen in the 70s and 80s. I have no idea why. But see the data for yourself: https://data.london.gov.uk/dataset/population-change-1939-2015 https://data.london.gov.uk/dataset/population-change-1939-20...