It clear that Azure bandwidth is being throttled in the UK. The solution is to use a VPN to somewhere in North America. Many, many users have seen a dramatic improvement in 2024 install times (literally from hours to minutes).
Edit:
The VPN will not be needed permanently. Seb has explained there is install data in a large database that is cached. Prior to release it was tested with a simulated 200,000 user load. However with extreme load the cache is overloaded and it collapses, making all installations stall at 97%.
Asobo were forced to add a queue and then lockout geographic areas to reduce load and stop the cache collapsing.
With technical improvements to the database cache and a natural reduction in installs the need for a VPN to get over the 97% hump will diminish.