It's not the download that's normally the problem with the lockdown related over-utilisation, it's mostly the upstream connection. Despite the high speeds VM happily sell, most households don't come anywhere near maxing out their download speed (except when they do a speed test, or are doing a large file download). The upstream capacity is much lower, so it is much much easier to use a good proportion of your upload allowance through two or three people using video-conference like services for school or work. Because almost all networks (power, water, roads, telecoms) are designed with less capacity than if everybody wanted to use them at once, the network architecture is designed around assumptions about only providing a fraction of the cumulative capacity, and because of the unusual circumstances of lockdown those calcs have proven to be wrong for VM's upstream in many locations (but not all, my connection has been fine). By various flukes of technical history and regulation these same considerations don't apply as much to Openreach, but obviously there's other different downsides there.
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