I'd guess that your experience is somewhat out of date. In London €* arrives at St Pancras. From there and Kings Cross which is adjacent its possible to get direct trains to about half of mainland UK (Example Destinations Brighton, Gatwick Airport, Cambridge, York, Newcastle, Edinburgh, Aberdeen, Inverness, Luton Airport, Leicester, Derby, Sheffield, Leeds). Euston station which serves Birmingham, Manchester, Liverpool and Glasgow and the Irish ferries is about 10 minutes walk or a short cab ride away.
The infrastructure and services are all in place and London is a much better connected city than Paris.
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