[Jonesy55]

In addition to the examples already given of Glasgow and London, most larger industrial cities in the UK saw big falls from peaks in the inter-war years up to the 1980s/90s. In all cases there was also a big corresponding increase in the populations of new suburbs outside the city limits as family sizes fell and the worst inner-city slums were torn down. I don't think any urban area including both city proper and suburbs saw a decline of such scale though.