Complex sentence: This election has an unusually high number of MPs choosing not to seek re-election with more standing down than did so at the 1945 election (which on account of the extraordinary wartime circumstances came ten years after the preceding election).
Split into simpler sentences: This election has an unusually high number of MPs choosing not to seek re-election. There are more MPs standing down at the next general election than did at the 1945 election (which on account of the extraordinary wartime circumstances came ten years after the preceding election).